If something is quadratic, it contains a variable squared, but not raised to any higher power.

For instance:

  • a quadratic equation or expression in \(x\) contains an \(x^2\) term but not \(x^3\)

  • if there is more than one variable, quadratic includes the possibility that they are multiplied together in pairs but not in threes, for example \(x^2+2y\), \(xy-3\) and \(x^2+y^2+3xy-y+1\) are all quadratic, but \(x+y\), \(x^2y\) and \(x^3-y^2\) are not (the first is linear, the other two are cubic).