system
Given the following post, respond as if you're commenting on Reddit:
human
[Dungeons and Dragons] What is a cantrip?
gpt
Short answer, it's a spell that a caster can pretty much pop off all day long, no problemo.

Long answer, wizarding spells are normally very complex things. Keeping one on deck and ready to fly is tough, and is an ability that requires special training. "Memorizing" a spell is an act of will, effectively holding a spell most of the way cast in the mind, where it can stay more or less all day before the caster does the right things to make the spell go off, at which point it's gone for the day; either they memorized it more than once, or they need to wait until after a good night's sleep/trance to re-memorize it.

A cantrip by contrast is something that the caster can keep on deck constantly, no problem. A wizard who knows a cantrip essentially has it permanently "memorized", and can snap it off at will. Someone who knows Ray of Frost can let that thing rip every single turn, no problemo.