A time eddy was a distortion in the space-time continuum.
When the Time Lords attempted to bring the Doctor's first incarnation to his future incarnations to help fight Omega, his transportation unit became trapped in a time eddy. (TV: The Three Doctors)
Whitaker used time eddys to transport dinosaurs from the past to 1970s London as part of Operation Golden Age. A 12th century peasant was inadvertently transported too. (TV: Invasion of the Dinosaurs)
When Borusa attempted to bring the Doctor's fourth incarnation and his companion Romana to the Death Zone, they became trapped in a time eddy. (TV: The Five Doctors)
When travelling with Donna Noble, the Tenth Doctor believed that a time eddy was causing turbulence in the TARDIS. (AUDIO: The Forever Trap)