A segment is one of several pieces that together create a whole. You could offer a segment of your orange to your girlfriend as a Valentine's Day gift. She’ll probably enjoy the orange, but she may break up with you.
Lots of things can have segments. You can talk about a segment of a talk show, a segment of a sphere, or the segment of students in your high school who want to join the Drama Club — the ones singing and dancing in the cafeteria every day. You can also use segment as a verb: when you chop down that oak tree in your front yard, you have to segment the trunk into smaller pieces for firewood.