YAML (YAML Ain't Markup Language) is a human-readable data serialization format that supports comments denoted by the # character. Single-line, inline, and block comments can be used to document intentions, explain values, and provide links to relevant material. Comments are useful for temporarily disabling parts of a YAML file or adding authorship and licensing details. Following best practices such as breaking long comments into multi-line sections, maintaining consistency in comment format, and using appropriate comment types can enhance the readability and maintainability of YAML files.