In the wild and left to their own devices adult cats typically do not meow. They communicate mainly by using body language, facial expression and scent. Cats are solo hunters and have no need to telegraph their prey's location. They don’t want any assistance in catching lunch. Adult cats usually limit their meowing to screeching and wailing cries when meeting an enemy or trying to attract a mate. These meows are not the same as those expected to emanate from the domestic kitty in the home. Kitty, though, is just as capable of producing a gut-wrenching primordial shriek should the need arise. A cat in great pain may let out blood-curdling shrieks whether it is feral or domesticated.
There are exceptions to the no meowing rule. Mother cats meow, trill and purr to their young. It is Mom-cats way of announcing her presence, calling wandering kittens back to the nest, warning of danger, and teaching her offspring the skills they will need to survive.
Why does the adult domestic kitty meow in the home if cats in the wild don't? It is us. We just don’t get it. Kitty discovers its complex system of scent, facial expression and body language does not get the point across to humans but sound does. Consequently kitty continues to use the vocal cues learned for communicating with mom. These meows seem to get humans' attention too. If a specific sound gets the required response then that is what the smart kitty will use for that request in the future. Adult cat language is still used cat to cat but when humans are involved the spoken meow is added. On the other hand cats may simply think humans have never developed beyond kitten-hood so behave accordingly.
Some cats habitually use the same sound but with different inflections and intensity. Others have a large variety of sounds in their repertoire. If kitty is ignored the meows are pretty much guaranteed to get louder and more intense regardless. There are cats that never seem to speak; it may simply be the silent meow. Kitty could have given up because its needs were never met. Some do not pick up the habit as no one talks to them. The latter aren't given the clues they need to communicate.
What do all these noises mean?
Happy sounds: A quick chirpy 'meow' is a standard greeting, the more of these strung together, the more excited kitty is to see you. Often used in conjunction with the chirrup and brrrp.
I want: The greeting may well change to the mid-length medium volume meow which is a request for something kitty suspects it wants; food, treats, open the door or and the like. When the meow becomes louder and drawn out kitty knows it needs something right now. If this fails to move anyone the mid-low pitch long meow is brought into play. Kitty is in full begging mode.
Not happy: A long low pitch almost growl is definitely a complaint. It is usually heard when attempting to administer medication, stuff kitty into the carrier or kitty is thinking about getting into a fight. Be careful, this is a warning.
Extremely not happy: Cross between a long high-pitch meow and a scream. Kitty is in pain, frightened, very annoyed or all three. The cat from down the street staring through the window at kitty may well trigger this sound. It is safest not to touch a cat that is in this sort of mood; it is liable to blindly attack.