The wheelbase of a vehicle is (at least) a pair of measurements which tells how far apart the front wheels are from the rear, and how far the left wheels are from the right.
Importance of Wheelbase Measurements
Vehicle designers must give careful consideration to the wheelbase, because it has a major effect on how the vehicle will perform. A longer distance between the front and rear wheels will decrease the turning radius, but make the vehicle easier to direct and more stable at high speeds. A lot of distance between the left and right wheels usually improves handling, but the extra width can have parking and aerodynamic drawbacks.