Amortized, blended, and unblended cost

Unblended cost is the simplest. It is the actual rate charged for each resource, with no averaging. Blended cost averages a rate across all usage of a resource type in a consolidated billing family. That gives one effective per-unit rate across accounts. It can also hide which account or team drives the spend.

Amortized cost solves a different problem. An upfront commitment payment, such as a reserved instance paid in cash, gets spread evenly over every day of its term. You see one steady daily number that reflects the discount over time. Without it, you see one large spike on the purchase date and nothing after. Check which basis a tool reports before you compare its numbers.