From time to time I'll mention things below. This list should make for a handy reference.
Abbreviations and Preferred Terms
DL/DTL - Down the line (view)
FO - Face-on (view), also called caddie view
RE - Rear (view), also called posterior view
Inclination to the Ground - Too many people use the word "spine angle." Your spine changes its flex throughout the swing. "Inclination to the Ground" or "Inclination" is a far better phrase.
Basic Motion = "Chip Length Swing" = Clubhead goes two feet back and two feet through (kinda like a chip)
Acquired Motion = "Pitch Length Swing" = Clubhead taken back until the right forearm is parallel with the ground and then parallel with the ground again on the follow through ("9-3").
Total Motion = Full golf swing.
Note that I define "chip" and "pitch" shots when talking about the short game differently than this. This use of "chip" and "pitch" simply relates to the way the wrists will work in these motions as well as the length(s) of these motions.
Ball Flight Laws
Science has revealed that the "old" ball flight laws are incorrect, and that:
a) the starting path of the ball is primarily and overwhelmingly dictated by the clubface angle at impact
b) the ball curves due to the relative difference, if any, between face angle and clubhead path at impact
We simply say this as "the ball starts roughly where the face is pointing and curves away from the path."
Nine Types of Ball Flight
"Draw/Hook" and "Fade/Slice" are interchangeable in the drawing below.
Italics represent shots that don't curve. If the golfer is lined up at his target, bold represent the most usable shots within each trio. I wrote an article here.
Positions or Alignments in the Golf Swing
"Trailing" and "Leading" refer to the direction of the ball when viewed from a face-on angle, with "leading" being the left side for a right-handed golfer. Top and bottom refer to the grip, with the "top" being the left hand for a right-handed golfer.
These "A" positions stand for "alignments" and will often be written as "P." Since launching 5 Simple Keys we've changed our use of these terms to "A."
A2: Club shaft parallel to the ground on the takeaway
A3: Lead arm parallel to the ground on the takeaway
A4: Top of backswing
A5: Lead arm parallel to the ground on the downswing
A6: Club shaft parallel to ground on the downswing
A8: Club shaft parallel to ground on follow-through.
A9: Right arm parallel to ground on follow-through.
Accumulators in the Golf Swing
1: A bent right elbow
2: Leading (top) wrist cock
3: Angle between shaft and lead forearm (expressed as rotation about that lead forearm)
4: Angle between lead arm and shoulders
5: The trail forearm and shaft (i.e. the wrist angle)*
* See this thread for more. It's not an official accumulator.
Each accumulator has a corresponding pressure point.
Pressure Points in the Golf Swing
1: The heel of the bottom hand where it touches the top hand or grip
2: The last three fingers of the top hand
3: The first joint of the bottom hand index finger where it touches the grip
4: Lead armpit (or where the lead arm touches the chest)
5: Trailing armpit*
* MORAD folks add this one. There's no corresponding accumulator but it lets them talk about the trailing elbow separating (or not) from the chest.
Shaft and Elbow Plane
In a one-plane swing the head and hands will follow or stay between two lines: the shaft plane and the elbow plane. Both can be seen here in green and red. Hands follow the shaft plane until the right elbow begins folding, at which point they move up to the elbow plane. Impact is somewhere between the two and the clubhead and hands should exit the far side of the body.
Swing directions describe the orientation of the baseline of the swing plane (also called the "horizontal swing plane" or HSP).
INward - For a right-handed player, an HSP oriented to the left. At A6 the clubhead is often right of the hands when viewed DL.
ONline - For a right-handed player, an HSP oriented relatively square to the stance. At A6 the clubhead is often covering the hands viewed DL.
OUTward - For a right-handed player, an HSP oriented to the right. At A6 the clubhead is often left of the hands viewed DL.
Use of PGA Tour Players
I support the use of PGA Tour players to teach something to someone, or to serve as a basis for comparison. For example, if someone needs to see a good example of a player pushing his hips forward or keeping his club on plane, a video can help.
I do not support the use of videos of PGA Tour players as definitive proof of any theoretical decisions. For every video you can dig up that shows one thing, someone else can dig up another video from another year or another angle that shows something else - often involving the same player. PGA Tour players are freaks of nature, and what they do, and are capable of doing, is often not proof of anything beyond their own freakish abilities. Arguments which devolve into "Yeah, well look at this video. See, he does it here!" don't help anyone. Unfortunately, it's an easy trap into which many fall, myself included from time to time.
Less reliable is what PGA Tour players say they do. Quite often, they're wrong. It's shocking really how often what they feel they're doing is either slightly or totally different than what science, video, or photos reveal that they're actually doing.