For a short summary,
1 - Brisket/Navel + Curing (with a specific spice profile #1) + Braised/Boiled = Corned Beef.
2 - Brisket/Navel + Curing (with spice profile #1) = Corned Beef + Extended Soak + Smoked (with spice profile #2) + Steamed = Pastrami.
Pastrami is a process, not a specific product, and many things can be "Pastramied". Examples would be poultry (goose, duck, turkey breasts), fish (salmon, sturgeon filets), lamb/mutton/goat (leg, shoulder), pork (loin or belly), etc. In certain parts of the Middle East, "Pastramied" camel is prized.
More often than not the pastrami found in the delis of large chain grocery stores are made from top or bottom round.