Definition of Portal
Portal - A Web site that provides a gateway to other Web sites. Eric Donald Hirsch, Joseph F. Kett, and James S. Trefil. The New Dictionary of Cultural Literacy: What Every American Needs to Know. Third Edition. Copyright © 2002. All rights reserved. Houghton Mifflin (Boston).
por·tal (pôr'tl, po-r'-) Pronunciation Key n. 1. A doorway, entrance, or gate, especially one that is large and imposing. 2. An entrance or a means of entrance: the local library, a portal of knowledge. 3. The portal vein. 4. A website considered as an entry point to other websites, often by being or providing access to a search engine. adj. 1. Of or relating to the portal vein or the portal system. 2. Of or relating to a point of entrance to an organ, especially the transverse fissure of the liver, through which the blood vessels enter. [Middle English, from Old French, from Medieval Latin porta-le, city gate, from neuter of porta-lis, of a gate, from Latin porta, gate; see per-2 in Indo-European roots. N., sense 3 and adj., from New Latin porta (hepatis), transverse fissure (of the liver), literally gate of the liver, perhaps ultimately translation of Akkadian ba-b (ekalli), gate (of the palace), umbilical fissure of the liver (next to the transverse fissure).] The American Heritage® Dictionary of the English Language. Fourth Edition. Copyright © 2006 by Houghton Mifflin Company. All rights reserved. Houghton Mifflin (Boston).

A time portal was a gateway though which a person could time travel. In the 31st century, one of the ways a Temporal agent could travel back in time was through time portals. When Daniels took Jonathan Archer to the future to protect him, he destabilized the timeline, destroying the future he knew. This also meant Earth never developed time travel technology, so there were no time portals to send Captain Archer back to 2152. (ENT: "Shockwave") James Kirk, Leonard McCoy and Spock traveled back in time to 1930 using the Guardian of Forever, an ancient Time Portal located on an ancient world. (TOS: "The City on the Edge of Forever") Kirk, McCoy and Spock later traveled back into Sarpeidon's past through a time portal which was controlled by the atavachron. The time period chosen was based on the verism tape that was at the time accessed. (TOS: "All Our Yesterdays") The alien inhabitants of Devidia II used a space/time portal to travel to nineteenth-century San Francisco. (TNG: "Time's Arrow") Time portals have also been found on the Bajoran world Golana. They belonged to a now extinct race. Molly O'Brien fell into one of these portals in late 2374. (DS9: "Time's Orphan") "Time Portal," Memory Alpha, the Star Trek Wiki [Retrieved on December 25, 2008]