"a drawer or place where things are heaped together in a disorderly manner," 1825, the first element probably a variant of Scottish glaur "to make muddy" (mid-15c.), perhaps from Old Norse leir "mud." Sexual (originally homosexual) sense from 1940s.
: A private glory-hole club makes a lot more sense
A hole between stalls in a toilet, through which the penis may be put for oral sex (1940s+ Homosexuals)