A microlecture is a short recorded audio or video presentation on a single, tightly defined topic. Microlectures are typically produced by an instructor, who might begin by drafting a rough script that includes an introduction, a list of key points to cover, and a conclusion. 

Start Here, or Introductory, videos are used to jump start students in a course.   Typical topics include introductions (professor, course), LMS review, syllabus review, and textbook review.

Best practices encourages faulty to assemble a(n) Start Here/Introductory module.

Weekly updates are brief (e.g., 60 - 90 seconds) videos are used to: recap a prior week's coursework, introduce a week's coursework, and - possibly most importantly - enhance the instructor/student relationship.

Explanatory videos are used to share further detail with students about difficult concepts, assignments, or upcoming events.

These videos ofter come from questions received from students on a repetative basis.

Overview videos are a great way to introduce a topic or chapter in a book.  Similar to how instructors may begin their lecture with a "big picture" overview, an overview video may share a conceptual perspective with students.

Other videos include a plethora of creative ways to enhance your courses with videos.