Time portal

From Memory Alpha, the free Star Trek reference

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")