A Short Turn (from the TTC website) - When a vehicle is behind schedule, a decision is made by supervisory staff to make a service adjustment. Short turn means the vehicle will not continue to the end of the route but will be turned to travel in the opposite direction to balance service on the route.
When this happens the driver announces, "This bus will now short turn at Queen." or wherever the planned turn around point is. You usually have a few stops to decide what to do. Often I choose to walk the rest of the way, depending when the stop is. Other times, I wait with the huge group of angry people for the next bus (or streetcar, because it happens on them too.)
I swear this is only a thing for the TTC. I never experienced it in Ottawa, or any city that I have visited and used transit it. It also happens to me all the time, and it is so annoying!