Design Patterns - I think there are a few obvious ones like Singleton and Bridge, a few non-trivial like Strategy and the rest are just historic artifacts for interviews
Underlying this is the idea of a Patterns Language for programming: the idea that specific problems can be categorised into general problem shapes, that a satisfactory solution that fits the shape can be named, and that communication is aided by discussion involving those names. The idea of the patterns language is still very much relevant today. Whenever a developer says “this can be a redux saga” or “we’ll use serverless for that”, they are naming a general solution that they believe fits the shape of their specific problem.