Portals are spheres linking one location to another for a short time. They are not reliable links like ports to the Net, because they usually don't last very long and are difficult to create. The User would call a portal a 'back door command'. It's a program that creates easy, unauthorized access to a system or program.
Portals require a great deal of energy to create. The only way to create a portal is by using a Tear. Portals come in all different sizes; they will be the same size as the Tear it was created from.
Portals are the only way to go back and forth from the Net and the Web. When the Guardian Key Tools fleed the infection of the Super Virus Daemon, they went into a dark realm of Cyber Space using black portals. This is also how they returned, it is not entirely known where they were.
There are very few ways to turn a tear into a portal. Guardians create portals by using their Key Tools. Some Super Viruses, like Gigabyte and Hexadecimal, are capable of creating portals if they have enough of their own energy saved up. Class-M Web Creatures are also capable of stabilizing a tear into a portal. If a Game Cube lands on a tear, it will automatically stabilize it into a portal. Once the Game leaves, the portal turns back into a tear.
Usually, once a portal is used, it will shrink out of existence and the tear does not reappear. The only known exception to this rule is the tear at the Edge of Beyond.