Identity vs Account vs Principal

Identity

It is something who you are. For example, I am Artist. That is my identity.

Account

An account is a digital identity or a digital container of all the things you have access to. You can access your account with a user name and password (hopefully MFA as well).

Principal

It's a special account your resources in your environment can use to execute task with based on the type of leverage (permission) you have given it. It can talk to different resources (write), it can also get to know other resources in your environment (read).