Even if you don't teach high school, you should be aware that high school and even middle school students are going to sites such as CrashCourse and other sites to review for school.
I am posting three examples from CrashCourse to give you an idea of how the videos work and their quality. I have sent some high school students to CrashCourse, and they reported the site was helpful.
Here are two for English classes: one on Emily Dickinson and one on Catcher in the Rye:
Here's one for social studies:
Check CrashCourse to see the collections of videos available. How do you feel about students using sites such as CrashCourse? Would you send your students to such a site? Should you as a teacher be aware of the kinds of videos available online to help students study? Do you provide a list of videos for your students to review at home?