A line is a continuous distance from one point to another. Some lines are straight. Some lines are crooked (not straight). Lines can take many different forms.
In these examples, the word "line" is a noun:
They’re standing in line.
At the end of a race, runners cross a finish line.
There’s a fish at the end of this line.
He had some very funny lines in his speech.
Actors have to remember their lines. (lines: memorized words spoken when acting)
The word "line" is often used as a verb and as a noun when organizing things or people:
Line up.
Get in line.
Try to stay in line.
It’s not polite to cut in line.
Customers form a line when waiting for service.
Write your name on the line.
Don’t color or make marks outside of the lines.
There are many expressions that include the word "line."
He’s getting out of line. (He’s causing trouble.)
Don’t step over the line. (Don’t do that; otherwise, you will face consequences.)
They have a lot on the line. (They are taking a risk.)
Lay it on the line. (Be honest.)
She’s just giving you a line. (She’s not being sincere or honest.)
This is in line with what we were thinking. (in line = closely matching)
There’s a fine line between those two things. (fine line = a small difference)
The President drew a line in the sand. (a line in the sand = a situation that can’t continue without a consequence or punishment.)
They’ve gone over the line. (Their behavior was really bad.)
It’s the end of the line. (Something is over–a project, a trip, a life.)