the.com/guideline

means A suggested rule or principle that guides decisions or behavior without the force of strict law.

from Built from 'guide' (from Old French 'guider,' to lead or direct, likely from a Germanic root meaning 'to show the way') plus 'line,' evoking a line laid down to follow — like a marked path or a boundary sketched on a map. The compound sense of a 'line to guide you' emerged as a natural, transparent coinage rather than an exotic borrowing — practical English doing what it does best, nailing two sturdy words together to make a third.