The two foci are necessary to define the location of an ellipse, but the shape depends on the eccentricity, which is related to the lengths of the two axes.
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the foci (2 focal points) and the distance between the vertices.
an ellipse.
The major axis is the line that joins the two foci (focuses) of the ellipse. If all you have is a picture of an ellipse and you don't know where the foci are, you can still find the major axis in a few seconds: It's the longest possible line that you can draw completely inside the ellipse, and it's the line straight across the ellipse between the two opposite "points of the egg".
a regular oval shape, traced by a point moving in a plane so that the sum of its distances from two other points (the foci) is constant, or resulting when a cone is cut by an oblique plane that does not intersect the base.
In Newtonian three dimensional space, two points can create a line, three to "define" it. In Einsteins "time-space", a minimum of four points are required.