Rights Managment product confusion

IRM is a set of controls and actions that can be applied to SharePoint, OneDrive and Exchange and is built-in to Office apps

"Information Rights Management (IRM) helps prevent sensitive information from being printed, forwarded, saved, edited, or copied by unauthorized people."

Azure Rights Management can protect documents by encrypting the contents and applying a policy that follows the document wherever it ends up, forwarded, uploaded, copied etc., the document is protected at all times.

IRM and Azure RMS are closely related:

"Azure RMS is tightly integrated into the Word, Excel, PowerPoint, and Outlook apps, where this functionality is often referred to as Information Rights Management (IRM)."

Azure RMS is the protection component of Azure Information Protection, which adds features like labelling, classification plus document tracking and revocation.  Azure RMS is included in some Office 365 plans, whereas Azure Information Protection either can be bought as a standalone service or comes with Enterprise Mobility + Security and Microsoft 365 Enterprise.

I asked a similar question during an AMA, about another related component, OME, in case it's of interest - What is Office 365 Message Encryption?.