Q: Context: The field of view is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.

Question: what does the term field of view mean? Let's give stream of consciousness first:
To answer the question, consider the following: The field of view is the extent of the observable world that is seen at any given moment. Therefore, the final answer is the extent of the observable world that is seen at any given moment.