Ok, I was hoping not to have to ask this as I am pretty sure it is a very basic question and I would rather have found the answer by osmosis than waste a post here but I have been wondering for long time now…
What are these hui-blah-blah cards I keep seeing referenced in the forum?
I think you are referring to ui-blah-blah, which is shorthand for lovelace interface, which is now the default display environment.
No, there seem to be versions of some (or all) the core cards that are prefixed with hui.
e.g. hui-entity-button-card
When I Googled, I came across a repo for the old Polymer UI.
Perhaps hui == Home Assistant User Interface??
Hass User Interface?
the hui- prefixed cards are what the built-in lovelace cards are called within the source code.
Thank you.
Why would anyone need to reference them directly?
to differentiate against custom cards that they were once based on
Rather than take on hooey they could’ve insisted all custom cards begin with foo
… I’ll let myself out now.
fooey! 
Don’t let the -bar hit ya on the way out.
… okay that was pretty good.
