Good question and one that not many people ever ask. IASs are the original international standards that weren’t used by many of the developed nations, and were there for countries that didn’t have their own set of accounting rules.
Following on from a full adoption of IASs by the global community, the IASs were updated/improved and where a new accounting standard was then developed/required it was now to be an IFRS. So the first one being IFRS 1, created to aid those nations adopting international rules in transitioning across from local rules to international ones.