Tactical speed is the ability of a horse during the race to adjust its position and race in multiple positions, without becoming flustered.
It's often said that horses with good tactical speed are the easiest to train, because it doesn't matter if they race at the front, near the back, or get caught out wide.
They'll always give their all in the final furlong.
"I know he's drawn in the car park, but he's got good tactical speed, so I'm gonna stick with him here."