From their website:
Ephemeral films are non-fiction films usually made for educational, industrial, or promotional purposes. The two classic ephemeral film collections found on the Archive are the Prelinger Archives and AV Geeks.
In addition to these classic collections, you may view guidance films from the post-World War II British government, drive-in movie intermission ads, and videos documenting the history of San Francisco from 1906 to the early 21st Century. Many of these films are available for free download.