A Portable Hole is an object that creates a "hole" through whatever solid surface it is placed against, enabling a character to reach through the surface in question to its interior or opposite side. It may be removed by peeling it edge-first off the surface, and from either side; when not in use, a portable hole resembles a round disc of fabric- or rubber-like material that can be handled, folded, or stored like any solid object.
Portable Holes occur primarily in animation, and are usually Played for Laughs. Expect some degree of Hammerspace or alternate dimensions if the writer attempts to seriously explain how they work; other times, they are simply powered by the Rule of Funny.
Portable Holes are functionally distinct from teleportation portals, but the two occasionally overlap, since teleportation portals are "holes" of a sort themselves (and Our Wormholes Are Different). They are also related to Bags of Holding and generally interact badly with them.
A TV commercial for Abilify antidepressant medication anthropomorphizes the main character's depression as a portable hole with eyes.
Yellow Submarine has the Sea of Holes, one of which gets peeled off like this and ends up in Ringo's pocket. The hole shows up in the live-action segment at the end where the real-life Ringo Star says he's kept it as a souvenir.
Was also a case of Getting Crap Past the Radar when he said "I've got a hole in my pocket." This refers to a situation where a man can access himself via said hole.
Who Framed Roger Rabbit featured Portable Holes as an Acme Product. During the film's climax, Eddie became pinned against a steel drum by a cartoon magnet while fighting the Big Bad; he freed himself by wrapping a Portable Hole completely around the magnet, causing the magnet to break in half.
Roger Rabbit's Car-Toon Spin gets a special mention for containing a real Portable Hole (of sorts.) It's a section of moving wall with a hole in it. An animatronic Roger holds onto it and drags it back and forth as you drive through it. Still cool trickery, though.
They Live! features a scene where the hero uses a device that creates a hole, so he can fall through the floor.
Star Trek Into Darkness: McCoy casually uses a portable hole to gain access to a prisoner in the brig (although it's possible this hole only works on the brig).
Used by Jarlaxle in this adventures with Artemis Entreri in the Forgotten Realms books. Oddly enough, it works more like the traditional cartoon portable hole rather than like the Dungeons & Dragons magic item.
Eddie Drood from the Secret Histories books has a portable door as one of his gadgets. Basically the same thing.
The Warehouse13 episode Love Sick introduces the artifact "Francois Villon's Inkwell". Not a round rubber or cloth Portable Hole, but spilling the ink on any surface allows a person to reach straight through it. It's used in the episode to allow a pair of thrown keys to pass through a plate glass window before the ink quickly evaporates leaving a perfectly intact window.
Dungeons & Dragons specifies a magic item called the Portable Hole, which functions similarly to the Bag of Holding but must be placed against a flat surface to work. It also details exactly what happens if the two items interact with each other:
If a bag of holding is placed within a portable hole, a rift to the Astral Plane is torn in that place; both the bag and the cloth are sucked into the void and forever lost. If a portable hole is placed within a bag of holding, it opens a gate to the Astral Plane; the hole, the bag, and any creatures within a 10-foot radius are drawn there, the portable hole and bag of holding being destroyed in the process.
Plot Holes are used for much this same purpose in Protectors of the Plot Continuum, and stabilized ones form the basis of much of the PPC's technology. For one thing, it's how they get to other continua in the first place.
A 1955 episode called "The Hole Idea" featured them as the invention of a scientist, later stolen by a thief to commit crimes with. In the end, the scientist tried to use one of those holes to rid himself of his wife but the Devil brought her back because even he couldn't stand her.
Roadrunner and Wile E. Coyote occasionally played with this trope as well. The most common of these is the classic Painted Tunnel, though fake scenes on canvas are also common. True to the Running Gag of the cartoons, the Road Runner always subverts the gag (usually by turning the painting into a portable hole) while Wile E. suffers its full effects (and sometimes more as trucks or trains have been known to come out of painted tunnels to hit him).
Ed, Edd n Eddy plays with this, along with several other tropes, in the episode "1 + 1 = Ed". At one point in the episode, Eddy falls into a hole, only to fall out of the sky from off-screen and back into the hole in an endless loop until Ed picks up the hole, leaving Eddy to crash into the now solid ground.
It should be noted that the "hole" was actually a piece of the fabric of reality, which Ed previously sliced out of thin air, with a saw. Yeah, it was a weird episode.
Subverted after everything goes back to normal. Eddy falls down a manhole, so Ed tries to pick it up and pulls a whole sewer pipe out of the ground.
Felix the Cat has one of these in his "bag of tricks". Possibly the Ur example.
The New Adventures of Winnie the Pooh had one episode where Pooh is trapped in a bubble that had a subplot where Gopher spent the whole day looking for the hole that serves as the entrance of his home.
Tiny Toons had an episode where Montana Max had a donut hole factory. The factory was harmful to the environment until the Toxic Revenger (one of Plucky Duck's alter egos) shut it down. Fortunately The Hero was as Crazy-Prepared as Bugs Bunny (see above).
One Pink Panther short had the Panther create an underground staircase at a construction site after a door accidentally fell on top of him. When he pushes the door back up, it hits a construction worker, causing him to fall into the stairway, at which the Panther moves it onto the wall of an unfinished building.
In Tex Avery's Homesteader Droopy, the Wolf gets rid of an angry moose by getting it to charge into a barn, then shutting the door and removing it (from a now-blank wall), folding it up a dozen or so times, and casually flinging it over his shoulder - where it hits the ground, rapidly unfolds and opens up, and the moose charges back out.