Jenny is a character from the TV series Doctor Who. She appeared in the episode The Doctor's Daughter.
Canon story line
The Doctor, Donna and Martha land on a planet that is caught in a civil war. One of the factions captures the Doctor and takes a skin graft from him. From this graft a machine makes a female clone of the Doctor. The clone is "born" an adult and its purpose is to be a soldier in the war. This clone is named Jenny.
Jenny dies eventually, but, after the Doctor has left, she resurrects and decides to explore space.
Jenny was played by Georgia Moffett, daughter of Peter Davison, the actor who played the Fifth Doctor. In March 2011 she gave birth to the daughter of David Tennant, who played the Tenth Doctor. At this point the 'Doctor's daughter' jokes are just lining up, possibly with an Inception reference thrown in somewhere.