What is the most number 1 movie?

I'm curious, can you help me understand what exactly is meant by the phrase 'the most number 1 movie'? Is it referring to the movie that has topped the box office charts for the longest period of time? Or perhaps it's the film that has received the most number one ratings or reviews? It's a bit vague, so I'm wondering if you could clarify what criteria is being used to determine this title and give me an example of a movie that might fit this description.