This literally means "the same tempo". A tuba player and I looked it up in high school and laughed -- "why would you need to tell us it's the same tempo?", we wondered. This term, however, comes with a connotation to it -- that being that the meter is going to change, but the conductor's beat should stay the same. That is, when one is switching from a 2/4 meter to a 6/8 meter, the beat will be at the same tempo but with different subdivisions.