what is glicko rd and how does an opponent rate?

Glicko RD is a statistical estimate of how accurate a rating is. RD stands for rating deviation. If your rating is 1000 and the RD is 100, then they are saying that your true rating lies somewhere in a band of 100 points on either side of 1000. In general, the more often you play, the more accurate your rating gets. The more you play, the smaller the RD. Your rating might not change but the RD might decline to 50 or less if you played often, meaning your rating is pretty accurate.

RD is very high for new players--as high as 200. It leads to larger point swings as new players ratings start off. It normally declines as a rating get closer to correct.

It used to be included on all the detailed stats pages but has been removed. Why isn't clear.

Chess.com uses the RD in determining how much any given game will change ratings.

https://www.chess.com/article/view/chess-ratings---how-they-work