Although there is no easy answer, as scrap yards often have their own grading system, it mostly refers to the quality of metal. For instance low-grade copper might be pipe or solid metal used in plumbing with around 94% purity; whereas clean, shiny and undamaged copper with 100% purity will fetch the highest price.
For alloys this will depend greatly on the raw materials percentage breakdown. If there is a higher percentage of a cheaper metal, the buying price will be lower.
The simplest way to find out is to speak to your local scrap dealer, who can identify it for you.