Some more precise terminology, relative to yesterday:

Parts of an IPv4 address are referred to as octets, and there are 4 of them. I suppose they’re called octets because they’re represented by 8 bits.

The network identifier (denoted by Y below) and host identifier (denoted by Z below) together make up the address, and the number of octets that each identifier has differs depending on the class.

Class IP
A YYY.ZZZ.ZZZ.ZZZ
B YYY.YYY.ZZZ.ZZZ
C YYY.YYY.YYY.ZZZ