Selwyn
In the Wicca/Neopaganism circles it's called Imbolc. It's one of the greater Sabbats (along with Beltaine, Samhain, and one I can't recall just now). :(
You might be able to find out more in
Margot Addler's Drawing Down the Moon (preferrable second or third edition).
Phyllis (aka Sidhe Uaine or
Gaia Euphoria)