A formal warning or penalty issued by the chair umpire for unsportsmanlike conduct. First offense is a warning, second costs a point, third costs a game, and it escalates from there. Racquet smashing, verbal abuse, coaching violations, and time violations all qualify. Some players collect these like they're going for a career record.
"That's racquet abuse. Code violation, warning, Mr. Kyrgios. The crowd laughs because it's the third racquet this match."