Cat hair grows to a genetically predetermined length, which occurs during a growth period lasting 60-90 days, called anagen. There is then a short transitional period called catagen followed by a rest period, telogen, which lasts between 40 to 60 days. The cycle then restarts.
I have relied upon the illustration from Cornell University to show a cross-section of a cat’s skin showing the hair shaft and hair follicle. There are lots of images on the Internet of the phases of hair growth but they all refer to human hair and skin. There is a great similarity (perhaps it is identical) between feline hair growth and human hair growth but for the sake of certainty I wanted to ensure that the source of the image is entirely dependable.
Because individual hair shafts are at different stages of the hair growth cycle shedding of the hair is gradual. It is the amount of ambient light which is the main influence on hair growth. Increased light stimulates a heavy spring moult.
Indoor cats live in ambient artificial light i.e. there are no seasonal differences and under these circumstances indoor cats often shed all year.
Contrary to what you may have read on the Internet about the various cat breeds, there is no such thing as a non-shedding cat. Unless of course you are referring to the hairless cats such as the Sphynx which goes through the same physiological process but there is almost no hair to shed. However, the perceived benefit is somewhat nullified by the Sphynx’s oily skin as the oils have no hair to be desposited on. The cat needs washing regularly. Also the lack of coat means that they have to be indoor cats.
SOME PAGES ON CAT ANATOMY