> Most of the other replies here say it’s all about size, and size does matter, but it’s not the whole story.
Originally the distinctions were (mostly) of purpose, but after WWI a series of treaties (mostly the Washington Naval Treaty and the First and Second London Naval Treaties) set out size, equipment, and numerical limits for various categories, so a whole lot of the interwar design and classification was based on gaming treaty limits, and the resulting naming patterns had a lasting influence that gradually faded.
Originally the distinctions were (mostly) of purpose, but after WWI a series of treaties (mostly the Washington Naval Treaty and the First and Second London Naval Treaties) set out size, equipment, and numerical limits for various categories, so a whole lot of the interwar design and classification was based on gaming treaty limits, and the resulting naming patterns had a lasting influence that gradually faded.