In short, the meter coupling shoe is on non-AI, AI and AI-S Nikkors (with only a handful of exceptions).
AI and newer lenses have a ridge on the aperture ring that couples with more modern Nikons. The coupling shoe is not necessary with post-1977 Nikons, but it's there for compatibility with pre-1977 ones.
AI-S lenses add compatibility with program mode and shutter speed priority shooting, although to my knowledge only the Nikon FA really takes advantage of this. One of the FG bodies has program mode too (the FG itself I think) and uses this. So does the F301/F501/N2000/N2020.
Autofocus Nikons (other than the F501/N2020) use the "CPU" contacts (what a terrible name!) on the lens and meter couple electronically. Some autofocus Nikons retain an AI coupling tab that couples with AI/AI-S Nikkors.
Non-AI Nikkors can be AI-converted (see Mr. White's site).