Hello Laurence,
Yes, your understanding of the pipeline group vs. pipeline difference seems correct. I got confused too just now, and had to go find the GitHub issue which discussed this: https://github.com/gocd/gocd/issues/7605#issuecomment-575600153
You’ll have to ignore the mention of the action “define” there, since it wasn’t implemented (as you can see in the comments that followed the one above).
If you are able to improve the documentation, please do: https://github.com/gocd/docs.go.cd/blob/master/content/advanced_usage/pipelines_as_code.md
Cheers,
Aravind