The name Caitlin is a girl's name of Irish origin meaning "pure". Caitlin and is often added to lists like Irish Baby Names and discussed in our forums with posts like "A brother or sister for little Jack or Olivia".
From the experts:
An Irish and Welsh form of Catherine, Caitlin was a boom name of the eighties, rocketing from obscurity (Americans first heard it via the wife of doomed poet Dylan Thomas) to the height of popularity in the space of a decade. The original name was gradually eclipsed by its myriad spelling variations -- Katelyn and Kaitlyn both soon topping it on the popularity lists.
Now, most forms of Caitlin, including this most-authentic one, have started to dip, though there have been thousands of girls named Caitlin -- and Katelyn and Kaitlyn ad infinitum -- every year for the past three decades. So, while Caitlin is certainly one of the loveliest variations of Catherine, it's been overused to the point of semi-retirement, at least in the U.S. Cait might be a short form.
Actor Breckin Meyer named his daughter Caitlin in 2003. Caitlyn Jenner also brought a renewed fame to the name, though she uses the -lyn variation.