In a nutshell, it means that teachers make videos of their lectures / lessons and post them online. (weteachwelearn.org)
Learning Management Systems let the learners watch videos of lectures, track their progress, chat with each other or with their manager, and find any other materials they need, like PowerPoint presentations or white papers. (growthengineering.co.uk)
In flipped classrooms, students watch online videos of lectures at home so they can work on classwork in school. (indianapublicmedia.org)