Como dizer "Ponto de vértice(matemática)" em inglês

As in "the maximum" or "the minimum" of a parabola? You can also call it "vertex", however a vertex doesn´t describe (define) if there´s a maximum or a minimum value of the parabola in question.
In other words, by using the word "vertex" it doesn´t say if the parabola is open downward or upward.

http://www.mathwarehouse.com/geometry/p ... rabola.php
http://www.tutorbrasil.com.br/estudo_ma ... imagem.php