The phrase "inside baseball" is a term used mainly in the United States. It usually refers to a detail-oriented approach to the minutiae of a subject, which in turn requires such a specific knowledge about what is being discussed that the nuances are not understood or appreciated by outsiders.
The term is typically applied to discussions of science, technology, sports, entertainment, business, law, politics, or related subjects of which the public has some general knowledge, but whose inner workings do not need to be known in order to understand the concept as a whole. For example, a film critic may write a movie review using insider jargon, or information which regular movie goers would have little knowledge of or even interest in (such as citing the director's previous themes expressed in their movies in relation to the one being reviewed, because of the director's fascination with a particular school of filmmaking, or technical aspects of filmmaking).