My own definition is that a pedagogical task is 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.