This can range from a single lecture on a specific topic, to a series of lectures to gain new knowledge in a field, to entire graduate level degrees offered by leading universities.
Websites abound that have online classes on demand. This can range from a single lecture on a specific topic, to a series of lectures to gain new knowledge in a field, to entire graduate level degrees offered by leading universities. You can even learn from professors on the other side of the planet via this method!