EN 1078 is the European safety standard for bicycle and roller skater helmets. If a helmet carries this certification, it means it has passed independent impact testing required to earn a CE mark—the official safety badge needed to legally sell helmets in the European market. Think of it as Europe's equivalent to the CPSC standard required in the United States.
The protection level EN 1078 provides is very similar to CPSC, though the specific testing methods differ slightly—such as the shape of the test rig and how straps are evaluated. For everyday road, gravel, or commuter riding, either standard ensures a solid baseline of protection.
You really only need to pay attention to EN 1078 if you're buying a helmet in Europe or purchasing from a European brand online. If you're in the US, CPSC certification is what matters most. Some helmets carry both certifications, which is great if you ride on both sides of the Atlantic.