Delta-V is the total change in velocity that a rocket experiences for a trip. You can use the rocket equation to calculate how big your rocket needs to be do gain that delta-v.

For example, for a rocket to get into orbit requires a delta-v of 8.6 km/s. To go from there to the moon takes about 4.1 km/s. You can plug a Specific Impulse of 350 and calculate the approximate size of the rocket needed with ease.

Mmm. Actually, delta-v is the generic term for any change in velocity (delta = change; v = velocity) in any mechanics equation. Any time you use the accelerator (or the brakes) on your car, or for that matter even the steering wheel, you will experience delta-v relative to the Earth and objects around you.

Now, I'm not saying that WolfKeeper's use isn't the coolest use around, no no.