Use of the term pre-roll in online advertising takes inspiration from the original sense of the word in the film industry, where pre-roll describes a period of time during which the camera rolls, but no action begins. The prefix pre- of course indicates ‘before’ (compare pre-war, precooked) and, correspondingly, it’s also in fact possible to have mid-rolls, which appear sandwiched between two halves of the selected video, and post-rolls, which appear right at the end. Pre-rolls are the most common variation however, presumably because they’re the only option which guarantees that no part of the video can be seen without watching at least some advertising.

Use of the term pre-roll in online advertising takes inspiration from the original sense of the word in the film industry, where pre-roll describes a period of time during which the camera rolls, but no action begins. The prefix pre- of course indicates ‘before’ (compare pre-war, precooked) and, correspondingly, it’s also in fact possible to have mid-rolls, which appear sandwiched between two halves of the selected video, and post-rolls, which appear right at the end. Pre-rolls are the most common variation however, presumably because they’re the only option which guarantees that no part of the video can be seen without watching at least some advertising.