Can manifolds be uniformly approximated by varieties in the way that continuous functions can be uniformly approximated by polynomials?
I got the idea from reading the Princeton companion to mathematics when it gave:
Theorem (Nash) Let M be a manifold in $\mathbb{R}^n$. Fix any large number R. Then there is a polynomial f whose zero set is as close to M as we want, at least inside a ball of radius R around the origin.