|A magical trap that will displace anyone passing over it to a random place on the same dungeon level.|
A teleport trap is a magical trap that instantly teleports any player or monster that walks on it to another location on the level, even if flying. Because they are an instantaneous form of teleportation, they make for good emergency escape routes, especially if you've already explored most of the current floor.
Temporary teleport traps are randomly generated, and are always visible. Once a player or monster has passed over it once, the trap will disappear. This includes if the subject was not actually teleported (e.g. a Formicid with stasis).
Permanent teleport traps are only encountered as part of a pregenerated vault, most notably the Hall of Zot on Zot:5. Like temporary traps, they are always visible, though as their name suggests, do not disappear.
Items on a permanent teleport trap are stuck and cannot be accessed normally, even with autopickup. You must use the Apportation spell or have the -Tele intrinsic (or be a Formicid) in order to retrieve it.
When uncovering dungeon tiles, you may randomly encounter sourceless malevolence that manifests itself as a teleport trap. Unlike the physical traps, the exploration effect will always teleport you next to monsters (if possible), similar to teleportitis. It does not have a physical presence.