Automatic Noise Reduction System. From the manual: "ANRS, compatible with Dolby B noise reduction, lets you play Dolbyized cassettes and make noise-reduced recordings."
JVC fought Dolby Labs over who invented noise reduction first, but apparently they were just trying to get out of paying royalties to Dolby. There was also Super ANRS, which was equivalent to Dolby C. Here's an article about it from January 1972.