For an explanation of all weapon properties, see Weapons.
Two-Handed is a weapon attribute; weapons with this property require two hands to use.
List of Two-Handed Weapons
Glaives
Greataxes
Greatclubs
Greatswords
Halberds
Heavy Crossbows
Light Crossbows
Longbows
Mauls
Pikes
Shortbows
Versatile weapons also have the Two-Handed attribute, and can be wielded with one or two hands.