A bit, which is short for "binary digit", is the smallest form of data on a computer.
Bits can only be 1 or 0. If a bit is 1, then it is "on" or true. And if a bit is off, then it is "off", or false. The concept of bits is based on Boolean Algebra.
The terms bit and byte are often confused. A bit is a single unit, and a byte is a group of 8 bits. The abbreviation for bits is "b", and for bytes it's "B".
These days, we measure larger units like storage size in bytes (MB for megabytes or GB for gigabytes). But for things like internet speed, we use bits (100 Mbit/s or megabits per second).