Prone
A prone character is lying on the ground, whether on purpose or not.
A prone creature has disadvantage on attack rolls.
An attack that is either a melee attack or made from within 5 ft. has advantage on an attack roll against a prone target.
A ranged attack against a prone creature has disadvantage.
A prone creature can spend half of their movement to stand up, ending the condition, or they can crawl, which costs them 3 ft. of movement for every 1 ft. they move.
Notes
An example of the prone condition:
A commoner is shoved prone by a zombie. Another zombie then rolls an attack against the commoner, rolling with advantage. A skeleton archer 40 ft. from the commoner then attacks the commoner, rolling the attack roll with disadvantage. Then a second skeleton archer moves to a spot within 5 ft. of the prone commoner, rolling its attack roll without disadvantage or advantage. While normally a point blank shot would have disadvantage, the advantage granted by being within 5 ft. of the prone target causes the roll to be made normally.