UK Horse Racing is, unfortunately, chock full of various abbreviations. Here is a list of the more commonly used abbreviations used within the site and the ratings.
A/E - Actual Return divided by the Expected Return.
Cls - A strong rating field in the ratings concerned with the horse's class ability.
DD - Draw Down. The largest drop from a profitable peak to a subsequent low in the profit/loss.
Frm - A rating modifier given to a horses' previous recent runs. Bigger is better.
HCP - Historical Class Performance
JC - Jockey & Course combination, i.e. how well this pairing do together.
Lst - A value given to the horse's previous race as a modifier. Bigger is better.
PNY - Probability of a bank going bust.
RAdj - Raw Adjusted rating which, basically, the Raw rating adjusted for weight and age.
TJ - Trainer & Jockey combination.
TJC - Trainer, Jockey & Course combination. How this trainer has fared at this course with this jockey.
TC - Trainer & Course combination.
A list of abbreviations of a horse's finishing position can be read in the Results Codes page.