To overlap usually means to or happen at the same time. "I have overlapping meetings" means that I have two meetings that while they might not happen completely at the same time, one goes into the other. In other words if I have one meeting at 7:00 that goes until 9:00 and one that starts at 8:30 they overlap. If they never overlapped they never happened at the same time. They also might be saying that one thing never got in the way of the other. Does this help? If not I can try to explain a little better.

overlap in a strict sense means 2 or more things lap over each other partially. Or to put it differently they cover the same area partially. just google for images of overlapping to get a graphical depiction of this. So 2 common uses of overlap in a metaphorical sense are 1) calendar entries. Mainly because how they overlap in the calendar, so you hear people say I have overlapping appointments or meetings etc.. Note: overlapping in this context normally means that meeting/appointment a doesn't finish until after meeting b has started. Normally in a manageable way i.e. just means you'll miss first 5 mins or so. If its longer or means you'll have to miss one then you normally call it a conflict. 2) Courses/areas of study, here the it is normal to talk about area/field of study, as such again it is typical to talk about overlapping fields of study. An example here is that biology and medicine are overlapping fields of study. i.e. they both cover a lot of the same stuff, this also typically means that they are complimentary. i.e. research in one can benefit the other.

It is difficult to say exactly without any context.