The phrase is not a standalone product or software. Instead, it refers to a highly common technical specification for exporting or preparing short video files.

: A short, lightweight video used to showcase a project, research paper, or digital asset. Organizations like the ACM UIST Conference require these short summaries to accompany research submissions. They are also used on stock asset sites like VideoHive to show customers what a motion graphics template looks like before they buy it.

H264 Video Preview After Effects Templates | VideoHive. Web Themes & Templates Code Video Audio Graphics Photos 3D Files. UIST 2015 Video Previews Details - ACM