In the case of a constant force, work is the scalar product of the force acting on an object and the displacement caused by that force. Though both force and displacement are vector quantities, work has no direction due to the nature of a scalar product (or dot product) in vector mathematics. This definition is consistent with the proper definition, because a constant force integrates to merely the product of the force and distance.
The SI units for work are the joule (J) or newton-meter (N * m), from the function W = F * s where W is work, F is force, and s is the displacement. The joule is also the SI unit of energy.