Licence free, What is an air rifle, What is a pistol?

[Turnup]

It clearly DOES define what an air pistol is it is an "Air Weapon" with a max of 6fpe which does not have either a barrel length of 300mm OR an overall length of 600mm.

That is crystal clear because an "Air Pistol" over 6fpe is section 5 prohibited ,
and the quote you have put up clearly states that if it is over 6fpe but has EITHER a 300mm barrel OR is 600mm overall it is NOT prohibited
Therefore either a 300mm barrel or an overall 600mm makes it NOT an "Air Pistol"

Note the quote does not use the term "Air Rifle" at all, (except in reference to sect 1) it says "Air Pistol" or "Air Weapon other than a pistol" so those are the only two definitions that matter (under legal limit)

How can you not understand what is written in Queens English right in front of your face ???

I think my understanding is rather better than yours.

That's not what it says. To be S5 an air pistol must be both over 6 fpe and fail one or both parts of the 300/600 rule.