Coursework is the work you do during a course of study — essays, projects, lab reports, presentations — that counts toward your final mark, instead of (or as well as) a big exam. British schools and universities use this word all the time: “40% coursework, 60% exam.” It is usually done over weeks and handed in by a date. In this meaning it does not normally take -s: you do coursework; if you need a number, you say a piece of coursework. American English often says assignments instead, though people will still understand. Though actually, students sometimes use it for any homework. Strictly, homework can be practice nobody grades; coursework is the work that goes into the mark. It is a school word. You would not call your job coursework.