It's short for Subtitles for the Deaf & Hard-of-Hearing. It does not display in the same way as Closed Captioning. Closed Captioning comes up in a black box on the screen, but SDH does not,
Due to space limits, some of the info was cut off: Cartoon # 73 is actually Crazy Mixed-Up Pup, & there is another cartoon called Sh-h-h-h-h-h. Also, the cartoons have SDH, & there are bonus features, including a special episode of the original Woody Woodpecker Show.