The rectilinear crossing number of a graph G is the minimum number of crossings in a straight line embedding of G in a plane. It is variously denoted rcr(G), cr^_(G), RCN(G), or ν^_(G). It is sometimes claimed that the rectilinear crossing number is also known as the linear or geometric(al) crossing number, but evidence for that is slim. A disconnected graph has a rectilinear crossing number equal to the sums of the rectilinear crossing numbers of its connected components.