Delta Time just means "change in time". In other words, the number of seconds or milliseconds which the last frame took to render, and the amount of time by which you must step your physics simulation forward for the current frame.
Ie, if your last frame took 16 milliseconds, then 16/1000 = 0.016 seconds, which is what you multiply "100 meters per second" (or pixels, or arbitrary units) by to calculate how far to move your object that frame.
Ie, if your last frame took 16 milliseconds, then 16/1000 = 0.016 seconds, which is what you multiply "100 meters per second" (or pixels, or arbitrary units) by to calculate how far to move your object that frame.