This is the 7012th most frequent French word.
marius
"Marius" is a French given name, not a common noun with a definable meaning.
In this sentence, 'Marius' is used as a proper noun, specifically a male given name, referring to a particular individual performing the action.
Marius porte un chapeau aujourd'hui.
Marius is wearing a hat today.
Here, 'Marius' again functions as the subject of the sentence, referring to a particular person by name whom the speaker encountered.
J'ai vu Marius au marché ce matin.
I saw Marius at the market this morning.
In this context, 'Marius' is used as the title of a film, indicating the name used creatively for the artistic work.