A time trace, or temporal trace, was a temporal phenomenon.
Creatures who were trapped in the same place but in a different second of a time trap left behind a time trace. These creatures could feel when other creatures, who were trapped in a different second, were around them, but they weren't able to contact them. They felt it when they were walking through the same place, even though they couldn't see the creatures.
In 2009, the Trickster trapped the Tenth Doctor, Clyde Langer, Rani Chandra, Luke Smith and K9 Mark IV in a different time than Sarah Jane Smith and Peter Dalton. Trapped in another second, Sarah Jane was walking through Rani Chandra — for her it was an empty area. Rani shivered and told the Doctor that it felt like someone just walked over her grave. The Doctor explained that Sarah Jane was walking there, trapped in a different second. He called this a time trace. (TV: The Wedding of Sarah Jane Smith)
Brastall had a TARDIS programmed to home in on the Fourth Doctor's time trace when a rogue vortex generated by temporal flux scattered his Time Ring. (PROSE: A Device of Death)
The Reborn Master theorised that his manipulations of the timelines confused the Doctor's TARDIS's temporal trace when he was expecting to capture the Doctor. (AUDIO: Master of the Daleks) Travel via time warp also possessed a time trace that could be followed. (AUDIO: We Are The Daleks)
Jack Harkness was able to track River Song, who travelled via vortex manipulator, using her time trace. (AUDIO: R&J)