Polynomial root
The root of a polynomial f is a value for x where the polynomial value f(x) is zero.
For example, if the polynomial [math]\displaystyle{ f(x) = 2x^2 + 10x - 28 }[/math] then [math]\displaystyle{ f(2) = 2\cdot 2^2 + 10\cdot 2 - 28=0 }[/math], so 2 is a root of this polynomial.
In fact, it can be seen that also -7 is a root of this polynomial.