What is momentum?
Most people's idea of momentum is the same as their idea of inertia; it is how much an object wants to keep going.  The heavier and/or faster it is, the more momentum it has.

Specifically, momentum or "p" is given by:  p = m*v

The unit of momentum then is Kg*m/s.
Personally, I'm surprised that is hasn't been named after some famous dead guy... like our name for Kgm/s/s is the "Newton".