Exercises, Exercise-tasks and Task

The figure may show the relationship between the three terms.

1. Exercise

Teachers wish to focus students' attention on individual aspects of language, such as vocabulary, grammar, or individual skills.

For example, "re-write the sentence by chaning the present tense into the past tense", "fill in the blanks with the appropriate form of given words", or some multiple choice questions focusing on specific language forms (grammar or vocabulary).

2. Task

Teachers wish to focus students' attention on the complete act of communication. 

For example, "students work in groups and then propose some suggestions for the school's newly-built playground (no language form restriction and students need to present their suggestions to the whole class in some way after discussion)"

P.S: Think about the four components of a task:

3. Exercise-task

This kind of activity comes halfway between tasks and exercises. It consists of a contextualized practice of language items.

For example, "an activity helps the students to master the present continuous tense by getting them to describe what is happening in a pictures"