Binary is a number system that only uses two numbers: ones and zeros. Computers operate in binary, meaning they store data and perform calculations using only ones and zeros. In other words, input such as mouse movements, keyboard strokes, and any other information that computers process are all converted to binary at the lowest level.
Because binary numbers are much longer than decimal (normal) or hexadecimal numbers, they are usually converted back to decimal or hexadecimal notation for human readability. For example, the number 75 can be represented as 01001011 in binary or 4b in hexadecimal.