I think it's the name of the inventor. The company that made the original Marr now makes the Marrette wire nut. By now, the name might be like kleenex is to facial tissue, but I'm not sure if anyone else makes that type of connector. When I went to school, they had specific instruction on not twisting the conductors unless one was stranded and the other solid.
I was going to say that only my northern neighbors seem to know about this type of wire nut. I never saw lots of these connectors but I was out in the field from 1976 to 1998 and I think I only saw maybe 2 dozen or so.