What do you call a video that is viewed by a mass group of people over a short period of time?

A video that is viewed by a mass group of people over a short period of time is referred to as a viral video. This term describes content that spreads rapidly across the internet, typically through social media platforms, attracting a significant audience quickly due to its engaging nature, humor, or emotional impact. Viral videos often capitalize on trending topics or challenges, leading to a surge in views as people share them with their networks, further amplifying their reach.

In contrast, a feature film is a longer, typically more structured narrative film that is designed for theatrical release, while a documentary presents factual information about a subject, aiming to inform or educate rather than entertain in the same way. A short film is just that—brief in duration—but it doesn't necessarily imply widespread viewership or shareability within a short time. Therefore, the distinctive characteristic of a viral video is its rapid rise in viewership and engagement across a large audience, making it the most fitting answer to the question.