It's the region covered by Rindler coordinates which if you have an inertial frame with coordinates \(t,x,y,z\) and an observer with constant proper acceleration \(a\) who passes through \(x=c^2/a\) at \(t=0\) is the region \(x>|ct|\).Can you give me a reference on "the Rindler wedge"? The only Rindler publication I've got is Rindler's "Essential Relativity", revised second edition.