At io9 they had a Q&A with Brian Green, professor of physics and mathematics at Columbia University and the co-director of Columbia's Institute for Strings, Cosmology, and Astroparticle Physics. As part of that Q&A he answered the question 'What, exactly, is string theory?'. He managed to answer that question, at least in a basic sense, in under 2 minutes and the video for that is below.
The Q&A was part of Green's announcement of World Science U which aims to be an online university, specializing in science for people of a variety of interest and education levels. I've included the introductory video for that below as well.
The video comes across a bit infomercialy but the website looks really interesting. It also appears to offer some free resources, though it doesn't say anything about the cost of the courses.
For anyone who doesn't already know Open Culture has a lengthy list of free online courses, including courses offering certificates.
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