It is often used in words to indicate:
* A person who holds power or authority: For example, "democrat" (one who believes in democracy), "autocrat" (one who rules with absolute power), "bureaucrat" (one who works in a bureaucracy).
* A system of government: For example, "aristocracy" (rule by the elite), "plutocracy" (rule by the wealthy).
So, when you see the prefix "crat" in a word, it often tells you something about power and authority.