An elongated surface-damage track produced when contact or an abrasive action displaces or removes material from glass.
GlassRenu · Educational illustration
Meaning and boundaries
A scratch is not defined only by whether a fingernail catches it, and the visible groove may not reveal the full extent of subsurface cracking.
Why it matters in glass restoration
Depth, crack morphology, glass type, location, and required material removal determine whether restoration is appropriate.