A ham is a person whose hobby consists of using special radio equipment to talk to other people with the same hobby, often people who are in other countries.
A ham actor is someone who acts badly, exaggerating every emotion and gesture.
PHRASE
（常指演员故意地）表演过火，夸张做作
If actors or actresses ham it up, they exaggerate every emotion and gesture when they are acting, often deliberately because they think that the audience will be more amused.