Question

What is the major axis of an ellipse?

Answer 1

Let's say you have an ellipse (here's a graph as a visual).
graph{(x^2)/49 + (y^2)/25 = 1 [-12.88, 12.67, -6.04, 6.73]}
Imagine putting a point at the center of this ellipse at (0, 0). The major axis is the longest possible segment you can draw from one point on the ellipse, through the center, and to the opposite point. In this case, the major axis is 14 (or 7, depending on your definition), and the major axis lies on the x-axis.

If your ellipse's major axis was vertical, it would be considered a "major y-axis" ellipse.

(While I'm on this topic, the minor axis is the shortest "axis" through the ellipse. It's also ALWAYS perpendicular to the major axis.)