[gloftus]

Worth noting that the hyperbolic triangle in the article contains "points at infinity" which are not actually a part of the hyperbolic plane, so this is really an "improper triangle" as the article notes. One could construct a similar improper triangle in the Euclidean plane that consisted of two parallel lines meeting at infinity. Such a triangle would still have 180 degrees of internal angle but it's area and perimeter would be infinite.

[KuSpa]

However, by the fith axiom of euclid, the lines in your example cannot be parallel AND converge (not even in infinity). Thus, it's more an open rectangle.

Either they are overlapping which violates the definition of a triangle, or they don't and the parallel lines always maintain the same distance X to each other and consequently maintain distance X at infinity (let's say X=1, bc you can just scale it).