Vectors and scalars
A vector has direction as well as size; a scalar has size only.
A worked example
Walk 5 m east then 5 m west. Distance travelled is 10 m, a scalar. Displacement is 0 m, a vector, because you ended where you started.
The mistake people actually make
Speed is a scalar and velocity is a vector, so a car going round a bend at a steady speed still has changing velocity.