From SRD 5.2.1
Creature Type
Every creature, including every player character, has a tag in the rules that identifies the type of creature it is. Most player characters are of the Humanoid type. These are the game's creature types:
Aberration
Beast
Celestial
Construct
Dragon
Elemental
Fey
Fiend
Giant
Humanoid
Monstrosity
Ooze
Plant
Undead
The types don't have rules themselves, but some rules in the game affect creatures of certain types in different ways.