Plain English Meaning
It is a way for a control tower to land planes on two runways at once when those runways point in different directions and their approach paths cross. Special rules and procedures are in place so that if anyone has to abandon the landing, the planes will not run into each other.
Full Definition
An ATC procedure that allows simultaneous Instrument Landing System approaches to two different runways at the same airport whose final approach courses intersect at angles between 15 and 100 degrees. The procedure requires each runway to have its own ILS, dedicated missed approach procedures designed to diverge by at least 30 degrees, and specific and to ensure remain safely apart if either goes missed.