Jennifer is a Welsh name, very popular when I was born. My mother says it was the most popular name that year, but she didn't know it. It must be true, though, since nearly every year of my elementary school experience there were at least two other Jennifers and a Jenna in class with me. It made the teacher's job that much harder ;)
I was going to list a bunch of name meanings, but this page did it for me:

From http://dspace.dial.pipex.com/town/plaza/ge75/names.htm: Origin: Celtic. Meaning: fair and yielding. Possibly derived from the names Guenivere, Genevieve or Gwendolyn.

According to babynames.com: Meaning: White Wave. Origin: Welsh

From www.behindthename.com: Feminine. Cornish form of Guinevere.
Feminine. From the Welsh name Gwenhwyfar, which is composed of the elements gwen meaning "fair, white" and hwyfar meaning "smooth". In Arthurian legend she is the beautiful wife of King Arthur. Her betrayal of her husband with Mordred prompted the battle of Camlann, which led to the deaths of both Mordred and Arthur. Later versions of the legends tell of her adulterous affair with Sir Lancelot.

From : http://www.tbns.net/babynames/index.html: Origin: Celtic/Old English. Meaning: One who loves peace, Fair.

from www.babynamer.com: This girl's name is used in German and English. Its source is Gwenhwyfar, a Welsh name meaning "Pure and yielding, whitewave." The name Jennifer ranked sixth in popularity for females of all ages in a sample of the 1990 US Census. The name also ranked 14th for females born in the United States in 1994.