In the old days, televisions had a 4:3 aspect ratio.
Nowadays, 16:9 is the new standard.
When 4:3 content is viewed on a 16:9 screen, black bars are placed on the sides of the picture to make up the difference. This is called pillarboxing, an effect typically observed when viewing standard definition (SD) channels on a widescreen.
When 16:9 content is optimized for a 4:3 screen but is viewed on a 16:9 screen instead, the resulting picture has a black border all around. This is called windowboxing. Windowboxing wastes screen space so Philo zooms in on pictures where it is detected.