Byte

8 binary digits, where a single binary digit (called a "bit") can only be 0 or 1

Example: 10110110 is a byte

A bit can have 2 different values (0 or 1)
A byte can have 2×2×2×2×2×2×2×2 = 256 different values


Symbol is B (and b means bit)
Example: 1MB means 1 million bytes (or 8 million bits)