Just what is a monk?
Monks are masters of weaponless combat who have learned to harness their chi hurt their enemies or heal their friends. While they fight bare-handed, they can (and should!) equip weapons: they can use fist weapons, one-handed axes, one-handed maces, one-handed swords, polearms, and staves and can dual-wield one-handed weaponry. They use cloth and leather armor and, though monks originated in Pandaria (and you'll need the Mists of Pandaria expansion to play one), the class is open to pandaren, dwarf, human, blood elf, tauren, undead, draenei, gnome, night elf, orc, and troll.
They're a true hybrid class who can tank (brewmaster monks), heal (mistweaver monks), and DPS (windwalker monks). For resources, monks have health, energy (for brewmasters and windwalkers), mana (for mistwalkers), and chi. Chi is unique resource to monks: you have four possible points of it and start combat with zero. Some of your attacks will generate chi while others will use it, meaning monks take careful resource balancing.