A cat's 'meow' is not just a simple cat sound. It's actually a surprisingly sophisticated method of communication. A cat's vocalization habits and voice are as individual as the voice of a person. You may have a cat that hardly ever makes a peep or you may have one that's extremely talkative. Different breeds will have different sounding meows as well. For example, Siamese cats are famous for their particularly shrill wail.
The most common sort of meow is a plaintive cry for attention - if your cat is walking back and forth in the kitchen, she probably wants cat food
If meowing occurs when you've just come home, your cat is probably glad to see you and wants to be stroked or picked up - the welcome meow, particularly when it is repeated consistently, is also related to mating
A female cat in heat will meow constantly to advertise her availability to males - in some cats this can develop into prolonged wailing at all hours, day or night
Sometimes a cat will make strange chattering or even bleating sounds when discovering prey that's unreachable. No one is entirely sure why cats do this. Some suggest that it is simply a sound of feline anticipation or frustration, like someone smacking their lips. Some people even think it's a ploy on the cat's part to get its prey to investigate the strange noise. Growling, spitting, hissing and shrieking are all aggressive or defensive cries. Usually it's pretty clear if a cat is angry or frightened. Similarly, purring needs little explanation. It means your cat is content.
It should be noted that if you have a quiet cat that suddenly starts meowing or a loud cat that suddenly stops, it might indicate your cat is sick. You should pay particular attention if your cat starts meowing constantly while using the litter box, cleaning itself or eating cat food. Any of these could be signs of distress.