Slope mass rating is like a report card for how sturdy a mountain or hill is. Just like how your teacher gives you a grade, experts who study mountains use slope mass rating to give a grade to the stability of the mountain.
They look at a lot of things like how steep the slope is, how heavy the rocks and soil are, and how much water or snow is on the slope. If the slope is really steep, has heavy materials on it, or has a lot of water or snow, it might not be very stable, and could be dangerous.
The rating starts at 0, which is super dangerous, and goes up to 100, which means it's very safe. If a mountain has a low score, it might need to be studied more or even have structures built to help support it. So, just like a report card, the slope mass rating tells experts how well a mountain or hill is doing, and whether it needs help to get better.