Levitation
Version 0.11: This article may not be up to date for the latest stable release of Crawl.
Levitation is a status effect that lets you hover over the ground, ignoring most traps, water, and lava tiles, and gaining a bonus to stealth and carrying capacity. However, it does come with some drawbacks: you are more vulnerable to the Airstrike spell, you cannot pick up items, and you cannot descend stairs until the effect wears off. If you have the controlled flight intrinsic, you will fly instead, allowing you to ignore the last two of those handicaps.
You can achieve levitation through a potion of levitation, ring of levitation, or some artifacts.
History
Prior to 0.10, the Levitation spell allowed you to levitate.
0.12 will completely replace levitation with flight.