Spell Slot

Spell slots are magical energy reserves that spellcasters expend to cast spells. Regardless of how many spells a caster knows or has prepared, they can only cast a limited number of spells before resting.

When you cast a spell, you expend a slot of the spell's level or higher. Think of spell slots as containers of different sizes — small slots for low-level spells and large slots for powerful high-level magic. You can use a higher-level slot to cast a lower-level spell, and some spells become more powerful when cast using a higher-level slot (called upcasting).

You regain all expended spell slots when you finish a long rest. Some classes, like Warlock and certain Wizard subclasses, can recover spell slots on a short rest or through special class features.