Under the Rating heading in the Tactics Trainer, there's a row that says Glicko RD. Does anyone know what this is? Thanks.

Glicko is the system used to calculate the ratings here. RD stands for rating deviation.

For full details, read this article. Brace yourself for some stats though!

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

Statistics don't bother me. I'm a math guy. :-)

Thanks for the reference.