Self-contained Systems (SCS) is an architectural approach that separates the functionality of a system into many independent systems. Each self-contained system is an autonomous web application, and is owned by one team. Communication with other self-contained systems or 3rd party systems is asynchronous where possible.
As Eberhard Wolff explains in this episode, self-contained systems is not the same thing as microservices, but they are not mutually exclusive. Organizations often adopt a mix of architectural ideas, and it is worth understanding these different models so you can decide which of them to apply to your own projects.