This post will not be completed for a while. I'm going to start it now and keep adding to it until it is done. Reminder I'm using My System 21st Century Edition. So the diagrams numbers may not match if your using another version.
"A pawn is passed if he has nothing to fear from an enemy pawn in front of him ..."
Below is example #38 from the book. The pawns on a5, e5, and d5 are all passed pawns. The e5 pawn is blockaded.
Diagram #38 from the book.
Be sure to read the paragraph extolling the virtues of the pawn. Remember the points it makes that the pawn is best at checking the advance of enemy pawns, best at defending your own pieces, and can tie up pieces to keep them from advancing. Pawns should be respected.
In #38a below an example of how a pawn majority can come about. Nimzowitsch makes the point that if whites e pawn and blacks f pawn are exchanged the majority on the Kingside will be clearer.
A lot has to be considered but in general the point is that a pawn majority implies the threat of a passed pawn.
Diagram #39 Majority on the Kingside.
Diagram #40 The Passed Pawn is a criminal.
Diagram #41 Kolste - Nimzowitsch Baden-Baden 1925
Black sacrifices a pawn to create an outpost for his Knight. Then creates a battery behind the g pawn and advances.