Joseph Foley defines a task as "A Task-based approach to language teaching and learning looks at communicative knowledge as a unified system where there are communication tasks which focus upon the actual sharing of meaning through spoken or written communication."

FOLEY, J.  A Phycholinguistic Framework for Task-based Approaches to Language Teaching, Applied Linguistics, Volume 12, Issue 1, March 1991, Pages 62–75,

Richards, Platt and Weber (1986, p.289) define a task as "[a]n activity or action which is carried out as the result of processing or understanding language (i.e. as a response) … Tasks may or may not involve the production of language.  A task usually requires the teacher to specify what will be regarded as successful completion of the task."

Richards, J., Platt, J. & Weber, H. (1986). A Dictionary of Applied Linguistics. London: Longman.

Nunan (2006) defines task as "a piece of classroom work that involves learners in comprehending, manipulating, producing or interacting in the target language while their attention is focused on mobilizing their grammatical knowledge in order to express meaning, and in which the intention is to convey meaning rather than to manipulate form. The task should also have a sense of completeness, being able to stand alone as a communicative act in its own right with a beginning, a middle and an end (p. 17)." Nunan differentiates a pedagogical task as tasks which take place in the educational arena (Nunan as cited by Nunan, p. 14).”

Nunan, D. (2006). Task-based Language Teaching in the Asia Context: Defining ‘Task’ . Asian EFL Journal, 8(3), 12–18. doi: 10.1017/cbo9780511667336.002

Skehan (1998, p. 95) defines a task as “an activity in which:

• meaning is primary;
• there is some communication problem to solve;
• there is some sort of relationship to comparable real-world activities;
• task completion has some priority;
• the assessment of the task is in terms of outcome.”

Skehan, Peter. (1998). A cognitive approach to language learning. Oxford University Press.

Lee (2000, p.32) defines a task as:

“(1) a classroom activity or exercise that has: (a) an objective obtainable only by interaction among participants, (b) a mechanism for structuring and sequencing interaction, and (c) a focus on meaning exchange; (2) a language learning endeavor that requires learners to comprehend, manipulate, and/or produce the target language as they perform some sets of work plans” .

Lee, J. (2000). Tasks and Communicating in Language Classrooms. Boston, USA: McGraw-Hill.

Rod Ellis (2003) defines a ’task’ as follows:

 

'A task is a workplan that requires learners to process language pragmatically in order to achieve an outcome that can be evaluated in terms of content (rather than language). To this end, it requires learners to give primary attention to meaning and to make use of their own linguistic resources, although […] the design of the task may predispose them to choose particular forms. A task is intended to result in language use that bears a resemblance, direct or indirect, to the way language is used in the real world. Like other language activities, a task can engage productive or receptive and oral or written skills’ (Ellis, 2003, p.64).

 

Ellis, R. (2003). Designing a Task-Based Syllabus [Article]. RELC Journal, 34(1), 64–81. https://doi.org/10.1177/003368820303400105 (Links to an external site.)

Prabhu (1987:24) defines a task as "an activity which required learners to arrive at an outcome from given information through some process of thought and which allowed teachers to control and regulate that process

Prabhu, N. S.  1987.  Second Language Pedagogy.  Oxford:  Oxford University Press.

Bygate, Skehan, and Swain (2001) define a task as  “an activity which requires learners to use language, with emphasis on meaning, to attain an objective”.

Bygate, M., Skehan, P. & Swain, M. (2001), (Eds.). Researching pedagogic tasks: second language learning,
teaching, and testing. London: Longman.

Bygate, M. (2016) defines a ‘task’ as follows:

“Tasks are classroom activities in which learners use language ‘pragmatically’, that is, ‘to do things’, with the overriding aim of learning language.”

Bygate, M. (2016) Sources, developments and directions of task-based language teaching, The Language Learning Journal, 44:4, 381-400

Samuda and Bygate (2008) define a task as "a holistic activity which engages language use in order to achieve some non-linguistic outcome while meeting a linguistic challenge, with the overall aim of promoting language learning, through process or product or both." (p. 69)

Samuda, V., & Bygate, M.  2008.  Tasks in Second Language Learning. Basingstoke:  Palgtrave Macmillan.

“...any structured language endeavour which has a particular objective, appropriate content, a specified working procedure, and arrangement of outcomes for those who undertake the task. ‘Task’ is therefore assumed to refer to a range of work plans which have the overall purposes of facilitating language learning from the simple and brief exercise type to a more complex and lengthy activities such as group problem solving or simulations and decision-making” 

Breen, M. (1987). Learner contribution to task design. In C. Candlin & D. Murphy (Eds.), Language learning tasks (pp. 23-46). London, UK: Prentice Hall.

Wills, D. says: ‘By a task I mean an activity which involves the use of language but in which the focus is on the outcome of the activity rather than on the language used to achieve that outcome’ (1990:127 )

Willis, D. 1990. The Lexical Syllabus. London: Collins.

Ur (1991, p. 123) defines a task in the following way: "A task is essentially goal-oriented: it requires the group, or pair, to achieve an objective that is usually expressed by an observable result, such as brief notes or lists, a rearrangement of jumbled items, a drawing, a spoken summary. The result should be attainable only by interaction between participants."

Ur, P. (1991). A Course in Language Teaching. Cambridge: Cambridge University Press.

Williams and Burden (1997) define a task as ‘any activity that learners engage in to further the process of learning a language’. Williams, M. and R. L. Burden. 1997. Psychology for Language Teachers: A Social Constructivist Approach. Cambridge: Cambridge University Press.

A task is basically defined as a goal-oriented classroom activity (Ellis, 2003; Nunan, 2006; Oxford, 2006; Prabhu, 1987; Willis, 1998) which requires learners’ use of target language, focusing on the conveying of meaning rather than on the practice of form (Ellis, 2003; Nunan, 2006; Skehan, 1998), in Rohani, S. (2013). POSITIVE VERSUS NEGATIVE COMMUNICATION STRATEGIES IN TASK-BASED LEARNING. TEFLIN Journal, 24(2), 158-179. Retrieved from https://ezproxy-prd.bodleian.ox.ac.uk:7316/docview/1627736570?accountid=13042Links to an external site.

Bialystok (1983: 103) suggests that a communication task must (a) stimulate real communicative exchange, (b) provide incentive for the L2 speaker/learner to convey information, (c) provide control for the information items required for investigation and (d) fulfill the needs to be used for the goals of the experiment.

Bialystok, E. (1983). Some Factors in the Selection and Implementation of Communication Strategies. In C. Faerch, and G. Kasper (eds). Strategies in Interlanguage Communication. London: Longman.

Shehadeh, Ali. (2005). Task-based Language Learning and Teaching: Theories and Applications. 10.1057/9780230522961_2.

Candlin (1987:10) defines a task as:  One of a set of differentiated, sequencable, problem-posing activities involving learners and teachers in some joint selection from a range of varied cognitive and communicative procedures applied to existing and new knowledge in the collective exploration and pursuance of foreseen or emergent goals within a social milieu.

Candlin, C. N.  1987.  Towards task-based language learning.  In Candlin, C. N. and Murphy, D. F. (Eds.), Language Learning Tasks.  Lancaster Practical Papers in English.  Lancaster and London:  Lancaster University.

Nunan (2010:138) defines that pedagogical tasks "describe what learners do in the classroom to activate and develop their language skills. Although these tasks are designed for the classroom, there should also be a connection, however tenuous, to
corresponding real-world or target tasks."

Nunan, D. (2010). A task-based approach to materials development. Advances in Language and Literary Studies. 1(2). 135-160.

Nunan (1989) defined task as, ‘a piece of classroom work which involves learners in comprehending, manipulating, producing or interacting in the target language while their attention is principally focused on meaning rather than form. Th e task should also have a sense of completeness, being able to stand alone as a communicative act in its own right’ (p10).

Nunan, D. (1989). Designing tasks for the Communicative Classroom. New York: Cambridge University Press.

“A  classroom  task is an  activity having  a particular goal  and it contains communicative  language use in the process. Because task has a certain relationship with the extralinguistic world, it goes beyond the common  classroom exercise. The type of discourse emerging from task is aimed to be similar to the one that emerges naturally in the real world (Ellis, 2000).”

Hismanoglu, M. & Hismanoglu, S. (2011) Task-based Language Teaching: What Every EFL Teacher Should Do. Procedia - Social and Behavioral Sciences 15.C: 46-52. Retrieved from http://solo.bodleian.ox.ac.uk/permalink/f/1lj314/TN_elsevier_sdoi_10_1016_j_sbspro_2011_03_049Links to an external site.

Estaire and Zanon (1994) distinguish two main categories within the broad task defintion: 'communication tasks' in which the 'learner's attention is focused on meaning rather than form', and 'enabling tasks', in which the 'main focus is on linguistic aspects (grammar, vocabulary, pronunciation,  functions and discourse).' 

Estaire, S. & Zanon, J. (1994). Planning Classwork: A Task-based Approach. Oxford: Macmillian Heinemann.