Reference
ATP analytics glossary
Every metric this API returns, with the formula, what it is for, and the specific way people get it wrong. Written from how these are actually computed here, not paraphrased.
The game that decides a set at six games all: first to seven points, two clear.
A match's result written set by set, games for the winner first: 6-4 3-6 7-6(5).
The last possible set of a match: the third in best of three, the fifth in best of five.
Games a player won divided by all games played in their matches: a finer measure of dominance than wins.
Our rating for every player, moved after each completed match by how surprising the result was.
The same Elo, counted only from matches on one surface: a clay rating, a grass rating and a hard-court rating per player.
What a tournament is played on: hard, clay, grass or (in older years) carpet, and whether it is indoors.
Two players' record against each other: every meeting, who won, and on what surface.
A walkover is a match never started (one player withdrew); a retirement is a match stopped after it began.
The tours' weekly list of players by ranking points, as ESPN publishes it: the top 100 to 150.