I always called it roof pitch, I did roofing from 1993 to 2013.
a roof slopes at 45 degrees is a 12/12 pitch. or just a 12 pitch. as the second 12 is just a given.
always called it pitch. like the “the roof is a 5 pitch”
I have never said " that roof is a 5 slope" as the slope refers to the angle of the roof. “it slops down on one side more then the other” or something like that.
If I said to any roofer " thats a 12 slope roof, its too steep to get up there" I would be called a moron for sure. if I put that in my report and any one see’s it they would think I’m stupid.
When I was in school for Architecture CADD we used pitch on the drawings to represent the steepness of the roof.