Melee Attacks

A melee attack allows you to attack a target within your reach. A melee attack typically uses a handheld weapon or an Unarmed Strike. Many monsters make melee attacks with claws, teeth, or other body parts. A few spells also involve melee attacks.
A creature has a 5-foot reach and can thus attack targets within 5 feet when making a melee attack. Certain creatures have melee attacks with a reach greater than 5 feet, as noted in their descriptions.

Opportunity Attacks

Grappling