Toroidal space-time distortion was a type of distortion in space-time. The first conclusive advances on such distortions were made at Cambridge, Massachusetts, Earth, in 2052.

In 2286, as part of his memory test, Spock was asked by the computer to identify where this happened, and who was responsible. He answered correctly. (Star Trek IV: The Voyage Home)

The script also specified that Ralph Seron was responsible, though this part of the answer did not make it on screen.
Toroidal presumably refers to the shape of a toroid, a doughnut-shaped object.