When you have inhibitions, you're self-conscious and maybe a little anxious. A shy child at a birthday party might have fun only after abandoning her inhibitions and joining a game of musical chairs.
An inhibition is a force that prevents something from happening—and often comes from you yourself. Shy people are often said to suffer from inhibitions. Some inhibitions are good, such as the one that prevents us from choking the life out of people we dislike. Other inhibitions, like the ones that prevent someone from ever enjoying himself, are not so great.