Speed
Speed is a monster property in NetHack, also referred to internally as movement rate. For every turn that passes a monster will gain its movement rate in "movement points"; if the monster has 12 or more movement points (defined as NORMAL_SPEED[1]) in a turn it gets a move that turn (and more than one if it has another 12 points remaning after this, etc.) Thus a monster with a speed of 12 gets one move per turn, a monster with a speed of 1 gets one move every 12 turns, and a monster with a speed of 18 gets 3 moves every 2 turns.
A very fast player (obtained through speed boots or a potion of speed) grants an extra guaranteed extra six movement points per turn, and one turn out of three another extra six movement points[2], thus having the player move with an effective movement rate of 20, or five thirds normal, giving five moves every three turns. A fast player (obtained through wands of speed monster, quantum mechanic corpses, etc.) grants six movement points two turns out of three[3], resulting in an effective movement rate of 16, or four thirds normal, giving four moves every three turns.
A monster with intrinsic speed (gained by e.g. a wand of speed monster) has four thirds their normal movement rate[4]; a slowed monster (by means of a wand of slow monster) has two thirds their normal movement rate[5].
Being encumbered reduces the player's effective movement speed after speed adjustments. A burdened player has three quarters their normal movement rate, a stressed player one half, a strained player one quarter, and an overtaxed player one eighth[6].
