It depends on what the context is on the sentence as a whole, such as, "You got a 77 for the exam." This would be most referred to as a grade rather than a rating. OR "I saw on Yelp this place got a 4 out of 5." This would be mostly referred to as a rating rather than a grade. In your case in 'A movie gets a 8 out of 10', most people would referred it as a rating than a grade. Both grades and ratings can be professionalized and opinion based meaning, for example, "A restaurant has received an A code from the ", this is more professionalized because an inspector thoroughly checks the restaurant and GRADES them on how clean the restaurant is. "This restaurant has received an 4 out of 5 on Yelp", this could be either professionalized AND opinion based by a food critic or just a regular person who ate at the restaurant. You just really have to read the sentence and understand what it is just based off the context. Sorry this was long hope it helps.