valve

Hey guys, The valve that goes to my washing machine is leaking when I open it. The leak comes from the black arrow in the image. I would like to know if the part circled in red is a nut that I can tighten to solve the problem. Note: I tried but that piece didn't move (maybe I need to apply more...

Ah, the joys of older home ownership (1974). We thought our major plumbing issues were dealt with when we got rid of our orangeburg sewer line and our rusted out galvanized supply line to our house. It's still galvanized under the house, but we live in a very dry climate and the pipes/joints...