Speed - if it is a comprehensive speed rating, it will encompass not only the final time, but early speed, and closing late speed.
Class - it is hard to really define, and people have differing viewpoints, but a good example is like when Anderson Silva toyed with Forrest Griffin on 8/8. Griffin is a former champ, is very hard-working, and can kick some tail, but he was OUTCLASSED. Similarly, there are some horses that are $25,000 horses that are running with $10,000 horses. That is a serious drop in class of competition. Big fish in a small pond.
Form - takes into consideration the results of the horse's last few races and/or workouts.
Last - A more precise rating of the last effort. Win? Place? Show? Trouble in the start? etc.
Connection - This first one is probably the trainer. The trainer is a key part of the horse's performance, much like a trainer in combat sports such as boxing and mixed martial arts is an integral component for the athlete's chances at success.
Connection - This connection is probably talking about the owner. Many stables/owners have patterns and tendencies that are noticeable. Some owners do well with young horses. Some do well with turf races, etc.
Line - This is a numerical rating based on the morning line, the "official" initial odds for a race. I have recently reduced my reliance on them. They are only a guide. Hell, only 33% of the favorites win.
Are you sure that "J" is not an "L" by any chance? It would make more sense. An "L" would stand for Lasix, a drug used to aid in a horse's race efforts. First-time Lasix substantially increases a horse's ability.
