The Collaborative International Dictionary
owner-driver \owner-driver\ n. a motorist who owns the vehicle that he/she drives.
WordNet
n. a motorist who owns the car that he/she drives
Wikipedia
An owner-driver in NASCAR is a NASCAR driver who owns the car they are driving. The practice has been established since the beginning of NASCAR in 1949. However, owner-drivers are almost nonexistent today. One exception is Tony Stewart, who won the 2011 NSCS title as an owner-driver, but he was only a half owner ( Gene Haas being the other half). The main reason that owner-drivers do not exist today is the expense and responsibilities involved, essentially having two jobs in one. Owner-driver is not to be confused with a driver who owns a separate team, such as Dale Earnhardt, who raced his own team but still drove for RCR.