Vmu - The miniumum demonstrated unstick speed at which it is possible to get airbourne on all engines and to climb out without hazard.
Vr - the (pre-planned) speed at which the pilot initiates rotation, to achieve V2 by the screen height even with an engine failure. The monitoring pilot calls "Rotate" at said speed and the Handling Pilot pitches up towards whatever the target pitch is.
Vlo - The speed at which the main gear lifts off. Will be higher than Vr as the aircraft will continue to accelerate between the nose gear and the main gear lifting. Not a speed used for planning purposes though.
There are lots of factors which affect and lots more interesting info about performance, but for that I'd have to write a book, not merely a prune post!