Noun
bright line (plural bright lines)
(idiomatic) A clear distinction in the context of a legal or moral judgment.
In these situations, there is no bright line between aggressive play and outright cheating.
Frankly, right is right and wrong is wrong, particularly when a parent is talking to a child. A bright line around moral responsibility is very important. Edgar Bronfman, Jr.
Now is the time to draw a clean, clear, bright line and say if you are engaging in speech over the Internet you do not have to check with your lawyer or your accountant. You are a free American, and you have the opportunity to engage in free speech over the Internet. John Doolittle