A melee weapon is any weapon intended for use in direct hand-to-hand combat in contrast to ranged weapons which act at a distance.
The term melee originates in the 1640s from the French word mêlée, which refers to hand-to-hand combat, a close quarters battle, a brawl, a confused fight, etc.
In-game, pressing the F key will do a quick stabbing animation with the melee weapon.
It can be equipped for "blade running" by holding F or hitting 3, from there the player can left click to stab. Another knifing animation can also be done when the player right clicks.
It can then be unequipped by scrolling or pressing the 1 or 2 keys to equip a primary or secondary weapon.