There are actually several different types of built-in unsubscribes in Marketo. They're all represented by fields on the person object, just like First Name.

All of these fields are built-in to your Marketo subscription. They are all boolean (checkbox) type. They can be used in Forms or Change Data Value flow steps.

Unsubscribed

This is used on the standard unsubscribe page. If a person checks this box, or clicks the unsubscribe link in an email, they will no longer receive marketing emails. They will, however, receive operational emails.

Marketing Suspended

This field is set by the user for placing people on a temporary unsubscribe. People can only attain this status if they are manually changed or a change data value flow step is utilized.

Email Suspended

This status blocks a person from mailings for 24 hours after a hard bounce occurs. After 24 hours, the person will become mailable again. 

Email Suspended will remain checked even after the 24 hour period is over, so you can refer to people who have historically been marked as such. To see if the person is mailable, simply calculate 24 hours after the moment of email suspension.

Blacklisted

Use this for competitors. They will receive neither operational nor marketing emails. They get nothing!