short subject vs moving picture

short subject and moving picture both are nouns.

Word	Noun	Adjective	Verb	Adverb
short subject	Yes	No	No	No
moving picture	Yes	No	No	No

As nouns, moving picture is a hypernym of short subject; that is, moving picture is a word with a broader meaning than short subject:

short subject: a brief film; often shown prior to showing the feature
moving picture: a form of entertainment that enacts a story by sound and a sequence of images giving the illusion of continuous movement

short subject (noun)	moving picture (noun)
a brief film; often shown prior to showing the feature	a form of entertainment that enacts a story by sound and a sequence of images giving the illusion of continuous movement