Warriors, also known as Warrior Cats depending on where you live, is a lengthy series of books written by several people under the pen name of Erin Hunter. As the name implies, it is essentially about groups of feral cats living in a forest and trying to survive. Despite residing in the children's section of most libraries, it contains large amounts of graphic violence, death, and themes of racism; especially in the earlier books. In many ways, it's easily compared to Watership Down.
It has a rather interesting naming system; characters from the main Clans have a name composed of two words, the first of which normally stays with them for life (often reflecting their fur color), and the second of which changes depending on their place within the Clan. Kits have their names end with -kit, apprentices with -paw, and leaders with -star. The more creative names normally belong to fully-trained warriors and medicine cats. Names are sometimes changed in other contexts, usually to reflect an injury that causes their old name to no longer fit. Cats not from the main Clans may have names that do not fit this system, such as Barley, Talon of Swooping Eagle, or Princess.