The phrase "tallest mountain" means the mountain that has the highest peak or summit compared to all other mountains. It is the mountain that reaches the highest point above sea level.
Sentences with «tallest mountain»
This dad goes the distance — climbing tall mountains to retrieve his daughter's heart's desire. (mamanista.com)
IS IT just a coincidence that all the world's tallest mountain ranges lie at low latitudes? (newscientist.com)