Design systems are an amalgamation of a lot of different ideas and that have evolved over time. They are influenced in large and small ways by style guides, pattern libraries, software development, and even architecture.
A Pattern Language is a book written by Christopher Alexander is about using patterns to plan and build environments. The concept of reusable patterns in software development has been highly-influenced by this book.
“Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in a way that you can use this solution a million times over, without ever doing it the same way twice.”
Style guides are a visual system for representing a brand or product across digital and print. These are usually tools for designers.
Pattern Libraries are a collection of styles, components, and patterns for digital products. These are usually tools for developers.
Design Systems are a collection of styles, components, patterns, and process for digital products. These are intended for designers and developers.