Spells have an attached duration, which come in different forms.

Instant:

The spell effect occurs immediately.

Set duration:

This duration will not change, and does not rely on continuous casting or concentration.

Concentration:

The duration will last up to a set time, unless the caster loses or drops concentration.

Concentration is a state of casting where the caster is putting an amount of effort towards keeping a spell active. If a concentrating caster is hit, they must make a Concentration Check, which is an Endurance Skill Check. The DC for this check is 10, or half of the damage taken, whichever is higher.

Continuous:

A Continuous duration requires the caster to continue putting effort into casting the spell each turn. If the target leaves the range or possible casting area of the spell, the spell ends. If the caster cannot meet the required AP Cost Upkeep of the spell at the start of their turn, the spell ends.