Any of a wide variety of exercises, activities or devices used in the language classroom for realizing lesson objectives is known as—

The correct answer is technique.

In language teaching methodology (specifically following Edward Anthony's framework later refined by Richards and Rodgers), language pedagogy is divided into three hierarchical levels: Approach, Method, and Technique.

1. Approach: This is the highest level, referring to the set of theories or assumptions about the nature of language and language learning.

2. Method: This is an overall plan for the orderly presentation of language material, based upon the chosen approach.

3. Technique: This is the implementational level. A technique is a specific classroom activity, exercise, task, or device used by the teacher to accomplish an immediate objective of a lesson (for example, a role-play, a flashcard drill, or a gap-fill exercise).

4. Syllabus: This refers to an outline or summary of the topics, structures, or skills to be covered in an educational course.

Since the question specifically refers to the wide variety of exercises, activities, or devices implemented inside the classroom to realize specific lesson objectives, the correct term is technique.