 This means that there is a function "U"(x), called a "potential," that can be evaluated at the two points xA and xB to obtain the work over any trajectory between these two points.It is tradition to define this function with a negative sign so that positive work is a reduction in the potential, that is 
where "C" is the trajectory taken from A to B.Because the work done is independent of the path taken, then this expression is true for any trajectory, "C", from A to B.