According to some sources it means 'Keeper of the keys', but it isn't a traditional name. Most traditional names have Latin, Greek, Celtic or Hebrew origins but, as far as I know, 'Kailyn' doesn't have any such origins. Many parents invent names or new spellings of names for their children, based on similar-sounding names. Many girls' names begin with 'Kay' sounds and end in 'Lyn', so it's inevitable that the name 'Kailyn' would emerge. If you want an origin, though, the closest 'real' name to 'Kailyn' is the Irish name 'Caitlin', supposedly meaning 'pure'. Kathleen, Katherine, Catherine and countless other variants are anglicisations of 'Caitlin', so if you want to call yourself 'Kailyn' as an alternative to Katherine, that would be fine. By the way, unlike in China, European and American families don't worry about the meaning of names. People usually choose children's names according to how they sound, because it's a family name, or simply because they like the name. The lists of so-called 'meanings' of names simply tell us the origin in Latin or whatever language the name comes from. This 'meaning' is not significant in the way that it is for Chinese names. The majority of westerners don't know or care about the origins or meaning of their names.

Apparently the name was first invented in the US in 1993 as a combination of "Kay" and "Lynn". -http://www.ohbabynames.com/meaning/name/kailyn/631

I'm fairly sure it's Irish.