What is "costarring"

Usage examples of "costarring".

Green had at one time been one of New England's most influential aerobics instructors even costarring once or twice, in the decade before digital dissemination, on the widely rented Buns of Steel aerobics home-video series and had been in high demand and very influential until, to his horror, in his late twenties, the absolute prime of an aerobics instructor's working life, either one of Mr.