What do you call when two lines have meet?

Answer 1

It depends what shape the lines meet in. If they meet in a triangle the point in which the lines meet are called the vertex.

In Geometry, this isn't precisely true, since there are no "lines" in a triangle, only line segments.

In Euclidean (standard) geometry, two lines can only:

(a) meet at a single "point"; OR

(b) never meet (they are parallel lines).

You could ask "what if they meet at several points?". In that case, there is just one line. A line goes on infinitely far in either direction. And if two lines meet at more than one point, they are congruent at every point, and are therefore both just the same line. It is impossible for two different lines to meet at two or more points in Euclidean geometry.