A word descrbing a Young Girl trying to grow up way to fast.
Matt: Dude, jen just fucked that 18 year old guy. Shes 14!
Dan: yeah dude, talk about jruns.
Exact source unknown, popular use dates to late 2004 on AnandTech forums, referring to an error often recieved when browsing or searching the forums. Sometimes used in conjunction with OMGWTF as OMGWTFJRUN
The server encountered an internal error and was unable to complete your request
JRun closed connection.