Short for
Trotskyist. Usually but not always an offensive term, used by opponents of Trotskyism of both left and right persuasions (usually as a descriptive noun, "
the trots").
In some settings, such as the National Union of Students, the insult is so pervasive that anyone to the left of Hitler is liable to be labelled a "trot" at one point or another, because the
NUS right-wing associate any challenge to their rule with a conspiracy allegedly initiated by a long-defunct Trotskyist group called
Socialist Organiser.
The term also crops up sometimes in anarchist and ecological attacks on Trotskyists. It is also occasionally used by Trotskyists themselves, apparently as a "reclaimed" term, only heard within the Trotskyist in-group, although this is contentious and some reject the term completely.
Its derogatory implications probably come from its associations with the trots in its other sense.