(0,0)

The origin. The point on the cartesian plane where both x and y are zero. The x-intercept of x=y, and the y-intercept of y=x.

The top-left pixel on a monitor

Also the (trivial)solution to any homogenious differential equation of the form

a(subn)*dy^n/d^nx + a(subn-1)*dy^(n-1)/d^(n-1)x....... = 0