Why are quadratic equations called quadratics?

The word "quad" generally means 4. Quadratics don't have 4 of anything. Can anyone explain where the name comes from?

From MathWorld:

The Latin prefix quadri- is used to indicate the number 4, for example, quadrilateral, quadrant, etc. However, it also very commonly used to denote objects involving the number 2. This is the case because quadratum is the Latin word for square, and since the area of a square of side length $x$ is given by $x^2$, a polynomial equation having exponent two is known as a quadratic ("square-like") equation. By extension, a quadratic surface is a second-order algebraic surface.

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