Task-based teaching is about creating opportunities for meaning-focused language use.

(Willis, 2008)

Task: An activity (or  technique) where students are urged to accomplish something or solve some problem using their language. Preferably, this activity is open ended; there is no set way to accomplish their goal.

Task-based learning: Teaching/learning a language by using language to accomplish open-ended tasks. Learners are given a problem or objective to accomplish, but are left with some freedom in approaching this problem or objective.

(EFL glossary, Bogglesworld ESL)

Read more

1. Jane Willis on integrating a task-based approach into existing textbook activities.
2. Mike Long on focus on form in task-based language teaching.