PLAIN-LANGUAGE DEFINITION
Poster frame
A poster frame is the still image displayed before or while a video is not playing.
IN PRACTICE
An example
A landing-page video can show the product in use before the viewer presses play.
What this does not tell you
The poster does not prove that playback works on every device.
Use the term precisely
When you use this term in a brief or report, include the relevant source, scope and assumptions. An example explains the concept; it is not a benchmark or a promise of results.