Concurrent lines
A set of lines or curves are said to be concurrent if they all
intersect.
at the same point. In the figure below, the three lines are concurrent because they all intersect at a single point P.
The point P is called the "point of concurrency". This concept appears in the various centers of a triangle.
See Centers of a triangle.
Because lines extend indefinitely in both directions, unless they are
parallel
they will intersect somewhere.
Therefore, all nonparallel lines are concurrent.
Rays
and
line segments
may, or may not be concurrent, even when not parallel.
Definition and properties of orthocenter of a triangle
Points of concurrency  the point where three or more lines intersect
Definition and properties of the centroid of a triangle
Definition and properties of the circumcenter of a triangle
Definition and properties of the incenter of a triangle
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