Shield

1st-level abjuration
Casting Time: 1 reaction, which you take when you are hit by an attack or targeted by the Magic Missile spell
Range: Self
Components: V, S
Duration: 1 round

An invisible barrier of magical force appears and protects you. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from Magic Missile.

Spell Lists. Sorcerer, Wizard

Source: Player's Handbook, Dungeon Master's Guide