A 50-50 grind is a grind that has the skater face toward, following the direction of the ledge or rail, with both trucks firmly planted and grinding the rail. A 5-0 is very similar but differs slightly as the skater will pop their tail, raising the nose of the board into the air and allowing the trucks to rise up off the ledge. To paint a picture, it's like a standard manual in the form of a grind.