Short, plain-English definitions of the terms that come up most often in our research and coaching articles.
A face-aim error is a consistent tendency to aim the putter face (or a club face) left or right of the intended target at address and through impact. Because the face angle largely dictates where the ball starts, even a small bias pushes putts off the intended start line every time you make an otherwise good stroke. It is distinct from a stroke-path fault, which is about the direction the head travels rather than where the face points. Most golfers with a face-aim error are repeating it faithfully, which is why it is worth measuring before rebuilding a stroke.
Strokes gained measures a shot against the number of strokes a benchmark group of players would typically need from the same distance and lie. Beat that expectation and you gain a fraction of a stroke; fall short and you lose one. Summed across a round, it shows where scoring actually comes from rather than relying on blunt counts like fairways hit.
Approach proximity is the average distance your approach shots finish from the hole, usually grouped by the distance they were played from. It is a simple way to track approach quality without needing full strokes-gained data. Shorter proximity means more realistic birdie looks and, just as importantly, fewer awkward up-and-downs.
The start line is the direction the ball actually sets off in, before slope or curvature takes over. On putts it is governed mostly by where the face points at impact, with the stroke path playing a smaller part. Confusing a start-line problem with a green-reading problem is one of the more common ways golfers practise the wrong thing.
More reading on the research blog.