Delineation or demarcation: marking or defining boundaries, either literally (drawing a line) or figuratively (setting limits).
会議で責任範囲の線引きを明確にした。
We clarified the demarcation of responsibilities at the meeting.
国境の線引きは両国の間で大きな問題になった。
The delineation of the border became a major issue between the two countries.
業務内容は書面で線引きしておくとトラブルを防げる。
If you delineate the scope of work in writing, you can prevent troubles.
The act of drawing a line between what is acceptable and what is not; used idiomatically to set standards or boundaries.
職場での許容範囲を上司と相談して線引きした。
I consulted with my boss and set clear boundaries for what is acceptable at work.
友人関係でも線引きは大事だ。あいまいにすると疲れる。
Setting boundaries in friendships is important too. If it's vague you get exhausted.
Colloquially, a ruler (measuring instrument). In some regions '線引き' is used to mean a straightedge or ruler.
すみません、線引きを貸してくれますか？この線をまっすぐ引きたいんです。
Excuse me, can you lend me a ruler? I want to draw this line straight.