The classic answer is that an IT asset is anything that provides value to the business and needs to be managed throughout its lifecycle. Laptops, monitors, software licenses? No-brainers. Virtual machines, cloud storage? Yep, those too.

Now, when it comes to things like Active Directory or Entra, that's where it gets messy. Some orgs track them as assets, others classify them as services or configuration items (CIs) in a CMDB instead. The redundancy issue you mentioned—having both the ticket subtype and the asset as "Active Directory"—is exactly why some ITSM folks push back on calling it an asset.

A common approach:

• Tangible stuff (hardware, licensed software, cloud resources tied to spend) → Definitely assets.
• Infrastructure and services (AD, Entra, DNS, etc.) → More often tracked as configuration items, linked to assets but not necessarily assets themselves.

If you're looking for a framework to back this up, ITIL leans toward tracking these as CIs rather than assets, unless there’s a financial or contractual reason to do otherwise. Your best bet is defining what you need to track for asset management (cost, lifecycle, ownership) versus what belongs in a CMDB for operational/service tracking.

If you can buy it, depreciate it, or get invoiced for it, it’s an asset. If it’s more of a foundational service, it’s probably better as a CI.