Ziti is a hollow, tube-shaped pasta, and it's also the name of a baked, cheesy dish you can make with ziti.
In Italian, ziti is short for maccheroni di zita, or "macaroni of the bride." This probably comes from ziti's longstanding popularity as part of a wedding buffet, particularly in Southern Italy. Italian-Americans most commonly use these fat little tubes of pasta in baked ziti, which always features tomato sauce and cheese, and often includes ground beef, sausage, peppers, or mushrooms as well.