90* Tube Elbow M.Bspp X F.Bspp

You've got it right. One end carries a male G 5/8-14 BSPP thread and the other is female, same size and thread callout. So it functions as an inline directional change while keeping the same thread type and size on both connections. Good fit for situations where you need a 90-degree turn without swapping thread standards.

Built as a 90 degree elbow, it’s meant to route a connection around a corner instead of running straight through.

That's correct. The 90° elbow has a 5/8" BSPP male connection on one side and a 5/8" BSPP female connection on the other. Both sides are G 5/8 - 14 callouts.