A time eddy is 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. (DW: The Three Doctors)

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. (DW: The Five Doctors)

When travelling with Donna Noble, the Tenth Doctor believed that a time eddy was causing turbulence in the TARDIS. (NSA: The Forever Trap)