drupal_render() is a function that renders HTML given a structured array tree with a specific structure.
drupal_render() renders HTML given a structured array tree, and it is usually called from within another function, such as drupal_get_form() or node_view().
Rendering arrays are a generalization of the arrays used from the form API. Differently from the latter, they don't use properties to validate the user input, but to render an item on a page.
