A time distortion was a disturbance in space-time, sometimes caused by anachronisms.
Cyber-Technology could detect the Doctor's TARDIS by registering the time distortion it created. (TV: Attack of the Cybermen) The Sixth Doctor was able to track the Rani based on this. (TV: The Mark of the Rani)
Time distortion was present in the Humanian Era, the Sensorian Era, and the Sumaran Era, caused when the Eighth Doctor rescued Charley Pollard from the R101. (AUDIO: Neverland)
The Eleventh Doctor could not land the TARDIS in 1938 New York because of time distortions. (TV: The Angels Take Manhattan)
Behind the scenes
Time distortions in the Time Vortex act as obstacles in the first and last levels of the online game Doctor In A Dash where, as with all levels, the Doctor's TARDIS (the player) races against a Dalek Flying Saucer, a Judoon rocket, and a Slitheen craft to find a Space-Time Manipulator.