#9

Signed-off-by: Chris Malley <[email protected]>

doc/implementation-notes.md

@@ -14,16 +14,18 @@ This section defines terminology that you'll see used throughout the internal an
 
 Standard terminology:
 
+* axis of symmetry - line that intersects the vertex
 * constant term - the term _c_ of _y_ = _ax_<sup>2</sup> + _bx_ + _c_
-* directrix
-* focus
-* line
+* curve - generalization of a line, whose curvature need not be zero
+* directrix - a fixed line used in describing a curve or surface
+* focus - a point on the interior of a parabola, used in the formal definition of the curve
+* line - a straight curve (geometric definition)
 * linear term - the term _bx_ of _y_ = _ax_<sup>2</sup> + _bx_ + _c_
-* parabola
-* quadratic
+* parabola - a plane curve generated by a point moving so that its distance from a fixed point (focus) is equal to its distance from a fixed line (directrix)
 * quadratic term - the term _ax_<sup>2</sup> of _y_ = _ax_<sup>2</sup> + _bx_ + _c_
+* roots - or real roots, zero or more point(s) where a polynomial intersects the x axis
 * standard form - see [model.md](https://github.com/phetsims/graphing-quadratics/blob/master/doc/model.md)
-* vertex
+* vertex - the highest or lowest point of a parabola, also it's turning point
 * vertex form - see [model.md](https://github.com/phetsims/graphing-quadratics/blob/master/doc/model.md)
 
 PhET-specific terminology: