Jennifer is a female given name; it became a common first name for females in English-speaking countries during the 20th century. The name Jennifer is a Cornish variant of Guinevere, which is a French form of theOld Welsh Gwenhwyfar (gwen: white, fair + hwyfar: smooth, soft). Despite the name's similarity to the Old English words jenefer, genefer and jinifer, which were all variants of Juniper and used to describe the juniper tree, there is no evidence that it was derived from these.
The name has been in use since the 18th century. Before 1906 the name was fairly uncommon, but it became popular after George Bernard Shaw used it for the main female character in The Doctor's Dilemma. It gained even more popularity in the 1970s. Though its popularity is often attributed to the novel and film Love Story, Jennifer was already the number 3 name given to baby girls in the United States in 1969, the year before the book and movie were released. Jennifer was the single most popular name for American girls from 1970 to 1984. It is also popular for Hispanic females. Since the early 1990s it has remained common, but considerably less so. Diminutives include Jen (Jenn), Jenny (Jennie, Jenni), and Jenna.
In contrast, "Guinevere" itself is at present a rather rare first name, considered "old-fashioned" - a fate shared with "Lancelot" and other Arthurian names (except for that of Arthur himself, still very common and popular).
The protagonist in the 1938 novel "Miss Pettigrew Lives for a Day" is very self-conscious about being named "Guinevere", which goes along with her being depicted as an unworldly curate's daughter who wears old-fashioned clothing and is very confused and intimidated by the world of 1930's London.