YAML is a common, human readable language for configuration. Defined as a recursive acronym "YAML Ain’t Markup Language," YAML is the common configuration language used by Kubernetes.
Kubernetes has popularized YAML configuration. Consequently, millions of engineer-hours have been spent debugging YAML. This process can be characterized as staring at a configuration file in an editor and counting the number of spaces and indentation of every line to discover where an errant, invisible space has caused a catastrophic failure.