Assembly language
In most computers, memory is divided up into bytes. Each byte contains 8 bits.  Each byte in memory also has an address which is a number that says where the byte is in memory. The first byte in memory has an address of 0, the next one has an address of 1, and so on. Dividing memory into bytes makes it byte addressable because each byte gets a unique address. Addresses of byte memories cannot be used to refer to a single bit of a byte. A byte is the smallest piece of memory that can be addressed.