What does NR stand for in rubber?

Could you please elaborate on the abbreviation "NR" and its specific significance in the context of rubber? I've encountered this term in various discussions related to rubber production and processing, but I'm not entirely sure what it stands for. Is it a reference to a specific type of rubber, a manufacturing process, or perhaps a standard within the industry? Clarifying its meaning would greatly assist me in understanding the nuances and intricacies of the rubber industry. Thank you for your time and assistance in this matter.