What is a "street address"?

Solution 1:

An (unqualified) address can be a post-office box or APO address or the like — any place that can receive mail. People often use "street address" when they need to be able to find a person there, e.g. for packages that require signatures.

Solution 2:

Sometimes, "street address" refers to your physical location at a finer level than city. E.g., "1313 Mockingbird Lane", without the city name attached.

But yes, usually it's just a retronym to distinguish it from mailing address (originally) and now e-mail address, web address, IP address, and so forth.

Solution 3:

'Address' on its own can refer to 'email address', 'website address' and 'street address'.

'Street' is, therefore, a specifier to 'address', indicating that 'mailing' or 'postal' address is required.