The term 'sphere of study' refers to an AREA of knowledge or expertise. It is a broad term that can encompass any field of study, from the sciences to the humanities. A sphere of study can also refer to a specific subject within a field, such as mathematics or history. The crossword solutions for this term are AREA, which is a four-letter word that can be used to describe a particular field of study. This term is often used to refer to a particular AREA of knowledge or expertise, and it can be used to describe both a broad field of study and a specific subject within that field.