Letterboxing

Strictly, letterboxing means bars above and below and pillarboxing means bars at the sides, though most people use the first word for both. In short-form it shows up when 16:9 footage lands in a 9:16 frame. You get black or blurred strips top and bottom, and the picture is squeezed into a band across the middle. It reads instantly as repurposed material. It also eats the part of the screen a text hook needs. Reframe the shot, crop in and accept the loss, or design the vertical layout on purpose.