system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference between a religion and a cult?

Related: When does a religion become a myth? (Ex. Greek mythology)
gpt
From a sociological point of view, a "cult" is simply a group of people with a particular form of worship.  If you go back to Ancient Rome, the people who worshiped at the temple of a specific god would be a cult.

In modern popular usage, the term specifically refers to fringe religions that are highly manipulative or destructive in nature, generally centered around a single charismatic leader.  The label is chosen not so much because of their size as how they're organized & how they act.