Collar is CIP-speak for the case neck. H1 and H2 are the case neck diameter near the schoulder and at the case mouth respectively.

G1 is the diameter of the throat (in front of the case mouth). G is the throat length. Alpha1 is the angle of the radial surface connecting case mouth and throat. Its 90 degrees if rectangular, or it is some other angle (for example 45) if chamfered. h and s (if defined) are the lengths involved from case mouth (H2) to throat; best explained by looking at the drawing. i is the half-angle of the steepness of the throat (forcing cone).

b is the width of a groove, N the number of grooves, u the twist and Q the minimum cross section of the bore.

Pmax is what we know as maximum pressure of the cartridge.

PK is 15% higher and came into use when testing of commercial ammunition became mandatory. Based on the number of cartridge pressure measurements and the standard deviation (variation of pressure among the measurements) it is possible to estimate an expected highest pressure. This computed pressure maximum of the tested ammunition must not exceed PK.

PE is the maximum pressure of proof rounds (25% above normal since introduction of the piezo method).

M is the distance of the drill hole from the base of the case.

EE is for extremely rare situations where a pressure barrel does not exist. Then a minimum bullet ernergy (EE) may be used for proof, because pressure is not known.

Edit: Fe is the maximum headspace a weapon may have (added to S). I do not know what exactly the meaning of delta L is.