What is guitar amp modeling?

Guitar amp modeling is a digital technology for reproducing the sound and feel of playing guitar through physical amplifiers.  This technology may be embodied in a piece of outboard gear, or as a software plugin for a digital audio workstation.  In recent years, guitar amp modeling has advanced to the point of being difficult to discern by ear from the sound of the amplifiers being modeled.  Some brands associated with advanced guitar amp modeling include Line 6, Fractal Audio, and Neural DSP.