Porta

Were you looking for Portal, the Forerunner complex? A Porta is a sphincter-like orifice embedded into the floors and walls of Flood Hives that acts as the Flood analog to doorways. Portas were sighted in the Flood-infested High Charity and in the Halo 3 Multiplayer map Isolation. .

Trivia

 * Portas may or may not be the doors on High Charity, covered in Flood spore sacs.
 * Portas have at least two 7 references in them, one being that portas are made up of 7 segments, and that there are 7 portas on the level Cortana.
 * The name, porta, comes from the Greek word porta, which means door.
 * This is a reference to the number 7.