when we want to know what a movie is about, at the simplest level, we might be asking simply for what happens. In that case, we are asking for a film synopsis:

FILM SYNOPSIS:

• "Recounting the plot of a movie, telling what happens"  
• A basic summary of a movie that includes key plot developments
• typically a summary avoids mentioning the film's conclusion or any details that would spoil the film's intended surprises or twists
• this is why we sometimes see "SPOILER WARNING" 

but sometimes are interested in what a movie is about, the meaning of a film, at a more complex or deeper level. In those cases, we write or turn to TWO different kinds of written responses to movies:

FILM REVIEW (or film criticism):

• "A review... typically includes personal impressions and evaluations of a movie's content and techniques. A good review may touch superficially on topics that might be explored in greater detail in a formal analysis."
• Film reviews often help readers to decide whether or not to see a film by arguing for its achievements and/or shortcomings.  
• Typically published in mass-media outlets (newspapers, tv shows, magazines) for a broad general audience

FILM ANALYSIS (or film theory):

• "An analysis attempts to determine how the film uses various cinematic techniques and elements of narrative form to make a viewer react in a certain way"
• Film analysis considers the ways that a film might intentionally or unintentionally confirm, alter, or challenge cultural norms, ideas, and meaning. It attempts to understand how films participate in social meaning making, and is less concerned with evaluations about whether the film is "good or bad" in a traditional sense. 
• Typically published in academic journals/essays, or in smaller magazines/blogs, for a specialized audience.