In many university departments (within certain fields), a typical course will consist of a series of lectures and then some additional lectures given by teaching assistants (TAs). Suppose that we are speaking about a math department, then one of these TA lectures may typically be the TA solving some exercises, while the main lectures mostly focus on going through the course material. My question is, what do you call these additional lectures? Where I'm active (where English is not the native language), I've seen things like exercise session, supplementary lecture, tutorial, problem solving class, etc. Is there a "proper" word for it? What are these "lectures" (they're not lectures, because they are quite different from the (main) lectures of acourse) called elsewhere?
A commonly used term in the US is recitation (noted by Jim in comments). In the general sense, it simply means to present already learned material in front of an audience. But in the university I attended, large math lectures were accompanied by smaller recitation classes.
In some academic institutions the term is used for a presentation by a teaching assistant (TA) or instructor, under the guidance of a senior faculty member, that supplements course materials. In recitations that supplement lectures, the leader will often review the lecture, expand on the concepts, and carry on a discussion with the students.