Time dam

A time dam was a device used to stop time in certain areas. Queen Xanxia used time dams to prevent her death. Locking her true self in the last few seconds of her life, she created a "projection" of herself that was animated by her mind in the hope that the energy gained by Zanak mining other planets could stabilise her in the new form. However, the Fourth Doctor dismissed this idea as ludicrous, claiming that there wasn't enough energy in the universe to power the dams forever, even if Xanxia resorted to absorbing the energy from stars. The dams were destroyed when Zanak's Bridge was blown up. (TV: The Pirate Planet)

The Sixth Doctor encountered another example of time dams on a research station when recovering a Veltrochni data pod from a vault concealed behind two time dams. Unlike the temporal freeze used by Xanxia's dams, these dams first moved the vault an hour into the future — thus making it hard to break into something that wasn't technically there yet — and then moved the contents a day into the past, meaning that any theft attempt that actually gained access to the vault would be doomed from the beginning because the guards would have known about the theft since the day before. (PROSE: Mission: Impractical)