\begin{definition}[Definition:Parabola/Directrix]
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Let $K$ be an [Definition:Focus-Directrix Property of Parabola|parabola]] specified in terms of:
:a given straight line $D$
:a given point $F$
where $K$ is the locus of points $P$ such that the distance $p$ from $P$ to $D$ equals the distance $q$ from $P$ to $F$:
:$p = q$
The line $D$ is known as the '''directrix''' of the parabola.
\end{definition}