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vertex

The parabola's turning point — its lowest point (opens up) or highest point (opens down).

The vertex of a parabola $y=a(x-h)^2+k$ is the point $(h,k)$ where the curve turns around. It is the minimum value of $y$ when $a>0$ and the maximum value when $a<0$ .

Examples

$y=(x-3)^2+1$ has vertex $(3,1)$ , its lowest point.