a piece of work to be done, especially one done regularly, unwillingly, or with difficulty (https://dictionary.cambridge.org/dictionary/english/task)

A task refers to different types of activities that help with language learning. These activities can be simple exercises or more complex tasks like group problem-solving or simulations. The main goal of tasks is to make language learning easier and more effective(D Nunan 2004).

the term instruction is derived from the late Middle English word instruccioun meaning to provide structure and direction. (Random 2016)

Assignment is a task given to students by a teacher or professor, usually as a means of assessing their understanding and application of course material. Assignments can take various forms, including essays, research papers, presentations, problem sets, lab reports, and more.

activities are the observable actions of individuals, alone or in groups. This postulates that activity consists of overt be- haviour which can be described by verbs of action or position: to sleep, eat, talk, sit, hammer, walk, etc., but excludes verbs describing interior states as opposed to actions (to be in love, to be sad, to think, etc.) because it is not usually possible to infer with certainty intentions or interior states from observed actions (Jay Farbstein 1974)