Configuration.yaml language beginner's question

Beginner’s question:
I’ve seen many examples of configuration.yaml files.
Yet I don’t know what is the language is and what’s the the syntax for defining entities which are calculations based on other entities. I haven’t found the documentation or the reference for this yet.
Can someone tell me what this language is and point me to the documentation?
Thanks in advance

YAML for Non-programmers

Those are most likely Template entities…
HA: Templating
HA: Template Integration and Entities
Jinja2: Templating Engine Docs

Thanks very much Drew,
It was the Templating I was looking for.