The term "studio" in the context of a porn video tag generally refers to the production company or facility responsible for creating and producing adult content. Studios are where the scenes are filmed, directed, and edited. They often have their own unique style, cast, and content types they produce. In simple terms, it's similar to how Hollywood produces mainstream movies.
For example, popular porn studios like "Evil Angel," "Brazzers," or "Naughty America" are well-known for the type of adult content they create and their roster of performers. So, when you see a tag that says "studio," it usually refers to the production company responsible for producing that particular scene or movie.