What does it mean to be able to cast a spell “at will”?

Throughout the D&D 5e Player’s Handbook, particularly in the warlock’s Eldritch Invocations, there are abilities that allow the player to cast specific spells “at will, without consuming a spell slot.”

However, there is no detail given on what exactly “at will” is supposed to mean.

Am I correct in assuming “at will” means “does not consume spell slot”, and nothing more?