If something is provocative, it provokes a reaction. A provocative book might get people talking about a controversial idea. A provocative statement, such as "I hate babies," will get another kind of reaction.
The action, thought, or feeling is often a desired one, called forth on purpose. In fact, provocative is often used to describe actions or ways of dressing that cause sexual feelings. But provocative things can also call forth something unwanted: "She was angered by the provocative remarks." This adjective was borrowed from French provocatif, from Late Latin provocativus "calling forth," from Latin provocare "to call forth, challenge."