MOOCs are Massive Open Online Courses aiming to give everyone access to information and education.
For many of the courses, you don’t need any previous knowledge though an interest in and basic understanding of the subject matter is recommended.
There are many providers of MOOCs out there. Some of the better-known ones includeCoursera (all interests), FutureLearn (all interests), Udacity (mainly programming/Web development), edX (all interests), Stanford Online (all interests) and many more. Class Central consolidates most courses into a list that then takes you to the providers. A lot of universities and institutes offer short courses that are often introductions to their full-time taught courses.