The Blink spell is a 3rd-level transmutation spell that gives the caster a 50% chance per turn of blinking into the ethereal plane.
The main advantage of Blink is it increases the survivability of the caster. Removing them from the Material Plane means they cannot be targeted by spells or take physical damage.
The caster can also reappear in the material plane to a place they can see within 10 feet. This allows tactical battlefield repositioning.
Lastly, the Blink spell does not require concentration, so it cannot be broken and the caster can use other concentration spells.
Blink, does come with downsides. The most obvious is that it has a 50% chance per turn to do nothing, making it expensive for a 3rd level spell.
Lastly, as it is not a concentration spell, if the caster is knocked unconscious, they may continue blinking, meaning their allies cannot aid them.