A word, or exclamation, that can be difficult to define due to its context. The word can be used as a greeting when uttered quietly, usually accompanied by a nod or salutation. It can also have an expressive function, as an expression of anger or frustration. Used in this context, it functions as an abstract noun, as one may be in a state of 'wah'.
The most common usage of 'waah', however, is when a group of friends are driving along a high street and shout 'WAAH' at individuals or groups of people. This form of 'waah' serves no particular semantic meaning or purpose, other than scaring the public or exposing the nation to the 'waah' phenomenon.
*Group of friends driving down a high street* "WAAAAAAAAAAAAAAAAHHH"
Old Woman: *Drops her shopping and screams in fright*
Group of friends: *Laughter*
Plural & possessive: Waah's