In the early days, these chunks of addresses were split up in classes. The smallest class was the Class C, which would have 256 IP addresses. For example, 193.111.228.*, where * can be any number between 0 and 255. Bigger organizations such as universities would receive a Class B, for example 131.174.*.*. They could then split that class B into smaller class C networks for internal use. Some organizations were lucky enough to receive a huge pool, a class A. Stanford University used to have 36.*.*.*.
We will not go into the political discussion of the IP space shortage, but when it was deemed that this was a problem, people wanted to replace this system of network classes with something else. The problem of these classes was that a lot of IP addresses were wasted. If you needed 300 addresses, you could not use a class C, so you would get a class B, which contained 256*256=65536 addresses, of which 65000 would be wasted. The difference between a class B and a class A is even worse.