What is the origin of the idiom "old school" and when to use it?

The idiom "old school" originated from the informal use of the term "school" as a reference to a particular approach, style, or set of values. The phrase gained prominence in the mid-20th century and has since evolved to denote a preference for traditional or conventional methods, often with a sense of nostalgia. This expression is used to imply a commitment to established practices, principles, or styles that were prevalent in the past, contrasting with more modern or innovative approaches.