Binary code is the most basic form of data composed of 0's and 1's. A "0" or "1" is called a bit, and eight bits are called a byte, then 1024 bytes make a kilo byte and so on. The 0's and 1's are based off probability. This is the reason why 0 means False and 1 Means true.
This is a very generic simplified explanation. In it's essence it is a numerical system based on 2 (0,1), unlike the numerical system we are accustomed to which is based on 10 (0,1,2,3,4,5,6,