Pre-roll ads are video advertisements that appear before a featured video on a mobile device or a desktop.

They differ from post-roll ads, which are ads that appear after the video plays, and mid-roll ads, which play during the video.

A user often directly influences the content that appears in a pre-roll ad. For example, if the user visits a certain website or performs a certain online search, there's a greater likelihood that they see a pre-roll ad that relates to their search.