What does "solved analytically" and "closed-form solution" means?

*"Another class of interesting models that typically cannot be solved analytically are*

stochastic dynamic models of rational, forward-looking economic behavior. Dynamic

economic models typically give rise to functional equations in which the unknown is

not simply a vector in Euclidean space, but rather an entire function dened on a

continuum of points. For example, the Bellman and Euler equations that describe

dynamic optima are functional equations, as often are the conditions that characterize

rational expectations and arbitrage pricing market equilibria. Except in a very limited

number of special cases, these functional equations lack a known closed-form solution,

even though the solution can be shown theoretically to exist and to be unique."

What does "solved analytically" and "closed-form solution" means?