What does "interior" mean in this case? "In triangle ABC, point P lies in the interior of line segment AB." Suppose I say "In triangle ABC, point P lies in the interior of line segment AB."
Does that mean that P lies on AB or that it lies inside the triangle?
Thank you.
Edit: I saw this in 2019 AMC 10B Question 16.
2019 AMC 10B Questions
Sorry I cannot upload the screenshot of the question, it says something went wrong.
 A: The only reasonable meaning is that $P$ lies on $AB$, but it's not one of the endpoints. 
A: I would take it to mean that $P$ is on the segment but not the endpoints.  If $P$ is off the line segment there's not really any feasible way we can justify claiming it is in "the interior".
Where did you hear this said.  Was it a text or source you are supposed to take with authority?  Or something some person somewhere said?
I can see three interpretations all with problems.
1) It was a typo, and what was meant was $P$ was in the interior of the triangle.
2)  The person is triangle to express (very badly) the concept that if you extend perpendiculars to the segment at the endpoints, then the point $P$ will be between the two perpendiculars.  
Basically "Person 1: $P$ is between $A$ and $B$" Person 2: "You mean on the same line?" Person 1: "No not on the same line but between... you know, like, not way off to the side of $AB$ but between where $AB$ starts and where it ends".  Person 2: "But what does that mean?  That depends on the orientation".  Person 1: "Oh, you know what I mean".  Person 2: "No, I really don't".
This is a very bad definition and not at all a standard and not clearly stated.
In short, I'd declare this meaning to be ... wrong.
3)  $P$ is on the line $AB$ but not one of the endpoints.
This fits the Real Analysis definition of "interior" but not the intuitive first year geometry interpretation.  A line is one dimensional and doesn't have an "inside" if you view it in a two dimensional plane. 
This is the most sensible interpretation.  It's not standard... but the more I think about it, the more it seems a reasonable way to state "$P$ is a point on the line segment $AB$ that is strictly between $A$ and $B$ but not equal to either $A$ or $B$"  
It's usually implied when one says "$P$ is a point of $AB$" that $P$ is not $A$ or $B$. But that is not explicitly stated.  Saying $P$ is in the "interior" of $AB$ is not the worst way to state this.
So ... I guess that is what is meant.
