Time dam

A time dam was a device used to cancel the flow of time in certain areas, given enough energy. 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 to become fully corporeal. Xanxia claimed she had gutted her own world's energy to become immortal. 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, explaining the energy needed to sustain the time dams increased exponentially until she would eventually die because there would not be enough energy for her to scavenge. Her new body could never become fully corporeal as the premise of using a cell projection system to form a new body was false. The time 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)