In the Adult Industry, the phrase "Mainstream Production Studio," or colloquially "Studio" and/or "Mainstream" are all ways of referring to established brands who produce professional level adult content. Professional studios operate with multiple people on set and many departments working together to create the polished content adult consumers enjoy.
For example, in addition to the talent seen on camera, studios will have a producer on set filming, a production assistant or runner, and a make-up artist at minimum. After the scene is filmed, editors will splice and color grade, cut trailers and master tracks, and for larger studios, marketing will decide what content to use for social media and email campaigns. Some studios may even have their own dedicated web team who handles file storage and upload, custom website maintenance, and customer support for retailing their own content.