What does it mean for RFC 3339 to be "a profile of" ISO 8601?

RFC 3339 says:

This document defines a date and time format for use in Internet protocols that is a profile of the ISO 8601 standard for representation of dates and times using the Gregorian calendar.

The same terminology is used in this Stack Overflow answer comparing the two standards.

What does it mean for a document / standard to be "a profile of" another?

Solution 1:

In a comment, Mark Beadles sagely wrote:

You need to read ISO 8601, in particular ISO/WD 8601-2 Annex B, where the term "profile" is defined. It's not a regular English [meaning]; rather it's tech standards jargon.