Whether you giggle or chuckle or snort with amusement, what you're producing is laughter. Laughter is also what people hear when you laugh.
Funny movies, your friends' jokes, and absurd or embarrassing situations all cause laughter, which is the word for both the action and the sound of someone laughing. Laughter can be a silent, shaking movement, or a loud guffaw. There are a few other primates besides humans who experience laughter, and most babies can shake with laughter before they're even able to speak.