The Princeton University WordNet dictionary defines movie, film, picture, moving picture, moving-picture show, motion picture, motion-picture show, picture show, pic and flick all in the same way--as "a form of entertainment that enacts a story by sound and a sequence of images giving the illusion of continuous movement."
The term "picture show" has been around since around 1910, when the earlier names of this form of entertainment, such as "nickelodeon," "nickelette," "theatorium" and "nickelshow," fell out of the lingo, and the terms "moving picture" and "picture show" became the most common names for movies.
Today, the term "picture show" is considered old fashioned or unsophisticated. It is associated with the time period of silent movies or with rural people who come to the city and use the old-fashioned term.