Tesseract is a term to describe an area in space warped across multiple dimensions. A person who can create and navigate tesseracts is likened to a three-dimensional entity interacting with the second-dimension; while still limited by gravity, they can nonetheless perform remarkable feats such as moving through solid matter, transiting vast distances and literally turning space inside-out. Due to the massive power requirements, few are capable of harnessing the energy needed to create tesseracts. However, species such as the Pocket Universe species, the Magog, Celestial Avatars, and the Vedrans have shown some ability to do so. It should be noted that the Pocket universe species had to harness the entire energy output from a galaxy, while the Vedrans tesseracted the Ral Parthia solar system with Voltarium cannibalized from a Nova bomb.
In reality, a tesseract is a hypercube, a four-dimensional () cube. If a person could get to the fourth dimension, they would indeed be able to navigate common three-dimensional space the same way we can perceive the second dimension.