Is this a simple circle, with radius 1/2?

[seand]

I'm trying to understand this expression:
$$y=x^2+y^2$$

Using wolfram alpha it tells me this is a circle of radius 1/2

But to me I'm unfamiliar with this way of setting up a circle. Specifically the y on both sides of the equation is troubling me. How would you interpret it? Would you reduce it somewhat before interpreting it?

 

[Dick]

I would write it as 0=x^2+y^2-y and complete the square in y.

 

[seand]

Completing the square worked perfectly. Thank you.