In graffiti terminology, any surface (electric box, vacant store windows, garbage cans) that has been tagged by so many writers there is little or no space for more. Typically crews don't (or at least shouldn't) claim such spots due to the high traffic and freewall nature of these spots it would be arrogant to claim such a communal spot as your own crew's. This kind of spot varies from other spots because taggers may write over one another on a griller without an intentional "diss" on the other writer - most writers would consider it a diss though but it may be overlooked on a common spot such as a grilled box.
Guy 1: "Hey doggie wanna go catch some writes?"
Guy 2: "Sure fool I gotta go reclaim that spot i got dissed at"
Guy 1: "Man that's a grilled ass window i wouldn't worry about it"
Guy 2: "Well fuck it Ima murk that fool anyway!!!!"
Guy 1: "K"
"Homie that whole corner is grilled as fuck in every color!!!"