A time trap was temporal schism. Creatures were trapped within a single second, which looped continuously. Creatures who were trapped in the same place but at a different second left a time trace.
K9 Mark I recognised the bubble universe in which Omegon was imprisoned by the early Time Lords as a form of "time trap"; no true time passed inside it, although Omega could contain and shape the contents of the bubble with the power of his own mind. K9 believed that only the Time Lords could create time traps. (PROSE: K9 and the Time Trap)
In 2009 the Trickster, trapped the Tenth Doctor, Clyde Langer, Rani Chandra, Luke Smith and K9 Mark IV a different time than Sarah Jane Smith and Peter Dalton. The TARDIS was unable to fully materialise inside the time trap and appeared only for a very short time. K9 explained that the temporal schism was preventing the materialisation of the TARDIS. The time trap could only be closed when Peter Dalton withdrew his agreement with the Trickster. After this time was moving forward again. (TV: The Wedding of Sarah Jane Smith)