Mike Austin (YouTube video) explains what services are included in Azure AD Premium Plan 1 — examples named include single sign-on, password protection, and some conditional access — and clarifies that individual services inside Plan 1 (e.g., Conditional Access) cannot be purchased standalone; the buyer must acquire the Azure AD Plan 1 bundle.
Chapters
You can Google the differences between Azure Ad Plans. There's a whole chart that'll come up and show you the differences in those plans, and you can move through them and understand the differences there. But just note that the things here, within this dotted line and the brighter blue, are the services that make up an azure ad plan 1. That is things like single sign on, that is things like password protection. There's some conditional access included in there. Now, I cannot purchase any of those services that are inside that Azure AD Plan 1 as a standalone product. So if I just wanted, I don't know, say, Microsoft Conditional Access, I can't just buy conditional access from Microsoft. I have to purchase azure AD Plan 1. That is an example where a bundle is all that I can buy. I can't buy an individual product or service.