The term "crock" refers to a type of earthenware container or pot made from ceramic materials. These crocks are usually thick-walled, heavy, and durable, and they have been used for centuries as vessels for cooking, fermenting, and storing food.
Crockpots, or slow cookers as they are commonly known today, originally got their name from the material they were made of: crocks. Early slow cookers were designed with a ceramic crock as the cooking pot, and they were heated from the bottom by an electric heating element. The thick walls of the crock allowed for even heat distribution, making them ideal for cooking food slowly over an extended period of time.
As slow cookers became more popular and advanced, the materials used for the cooking pot also evolved. Today, many slow cookers feature cooking pots made of other materials such as stainless steel or coated aluminum. However, the term "crockpot" has remained in common use, even when the actual cooking pot is made of a different material.
So, in short, a crock is a type of ceramic container or pot historically used for cooking and food preservation, and the name "crockpot" originally referred to a slow cooker with a ceramic crock as its cooking pot.