The word bit has several meanings:

1. A small piece or amount of something. You might ask for a bit of someone's sandwich, or notice a bit of mud on your shoe. When you're working on a difficult puzzle, solving it bit by bit means making progress one small piece at a time. The phrase “quite a bit” means a fairly large amount, which sounds backwards but makes sense when you think about it: if you have quite a bit of homework, you have more than just a little bit.
2. The past tense of bite. Yesterday, a mosquito bit you. Last week, your dog bit into her favorite toy. The snake bit the explorer's boot but couldn't get through the thick leather.
3. In computing, the smallest unit of digital information, either a 0 or a 1. Your computer stores everything as millions of these tiny bits. Eight bits make a byte, and computers use billions of bytes to store photos, videos, and documents. When people talk about how fast their internet is, they often mention megabits per second, which measures how many millions of bits can transfer each second.
4. The metal mouthpiece on a horse's bridle that helps a rider control the horse. When you “take the bit between your teeth,” you're taking control of a situation with determination.