YAML stands for 'YAML Ain't Markup Language'. It expresses the same nested data JSON does (objects, lists, scalars) but uses indentation, dashes, and colons instead of braces and brackets.
It supports comments and multi-line strings, which is why it dominates config files: Kubernetes manifests, GitHub Actions workflows, Docker Compose, Ansible playbooks.
Watch out for the 'Norway problem': `country: NO` becomes the boolean `false` unless quoted. Always quote ambiguous strings.