Intangibility

Intangibility is the ability to alter the molecular structure of a person or object thereby lowering its mass and density to the point that it's molecules can slip between and through the molecules of another person or object. If the molecular dispersal is great enough, even light and gases may pass in between molecules. In speculative fiction, this is often demonstrated as a super-power common to ghosts, mutants and some species of aliens.

In the Star Wars mythos, when a Jedi dies, they may develop the ability to live on beyond their physical body as a force spirit. These beings exist in a permanent state of intangibility and can no longer maintain cohesive corporeal form. Obi-Wan Kenobi demonstrated this ability when he strode through the dense underbrush of Dagobah to speak with Luke Skywalker. For some reason however, he still felt the need to sit his wrinkly ass down on a fallen log. Go figure.

In Marvel Comics, the mutant superhero known as Shadowcat has the ability to render herself intangibility. She refers to this as "phasing". Shadowcat's intangibility is unique from other forms in that she can disrupt the electrical signals of technological equipment merely by phasing through it. This is a very advantageous ability to have, particularly when one faces up against robotic Sentinels.