Swords are melee heavy weapon introduced in the The Taken King expansion. Swords deals massive damage to a single target and it can also be used to block incoming attacks.
Note: Archetypes are sub-weapon classes within each weapon type. Guns of the same Archetype share fixed stat ranges on every stat. The stats are not the same for each gun, but all the guns in each Archetype will fall between the ranges of the Archetype. You can use this to get a better idea of what that particular gun is good at before you even look at it.