The name of an online video commercial that appears prior to an online video, it is typically :10 - :15 seconds in length. Once you click on certain online video links, you will be forced to watch a short commercial before the video content. This snippet of online advertising is known as "a pre-roll" or just "pre-roll" (as opposed to a mid-roll or post-roll).
Pre-roll looks the most like traditional TV commercials, and online advertisers claim it is better for three main reasons: 1) It has increased accountability (you are forced to watch it), 2) it targets a more engaged user due to its on-demand format (you clicked on the link to see it), and 3) it has a handy interactive component (you can take an action regarding the ad if you're interested). Some websites let you skip over the commercial spot, but most do not.
Pre-roll makes up a small percentage of the available interactive video inventory, but it is growing more popular due to the fact that online publishers can pretty much guarantee that users will see and hear the pre-roll commercial before the audio stream starts. It is also one of the simplest ways to utilize the Internet for sight, sound and motion.
NetLingo Classification: Online Marketing