What is the closed subscheme of $A^2_R$ defined by $x^2+y^2 = -1$?

Question

I have read the Scheme (mathematics).
The page says the following:
"The closed subscheme of $A^2_R$ defined by $x^2+y^2 = -1$ is a nonempty topological space."
But I don't understand the meaning of "The closed subscheme of $A^2_R$ defined by $x^2+y^2 = -1$" because of my lack of ability.
The definition of closed subscheme I know is:
https://www.encyclopediaofmath.org/index.php/Closed_subscheme
However I don't know more than the definition.
I'd appreciate if you could answer thisquestions.