What are A races vs others?

Your A race is the one you 'peak' for... your big race for the year that you focus all your training on. You can actually have a couple of A races per year...

It's a way of putting priorities on your races for the season.  "A" races are those that ae most important to you...where you really want to be at the top of your game.  You typically have only 1 or 2 "A" races during a season.  So for me, my 1/2 IM in September is an "A" race because it's kind of the big goal for me this season.