Would that be as in .41 AE?
If so, the AE stands for Action Express.
The cartridge was introduced by Action Arms in the mid-1980's. It is a true .41 caliber bullet, but the cartridge case has a rebated head the same size as a 9 mmP.
The cartridge was chambered in Action Arms version of the CZ 75, IIRC they were made in Italy by Tanfoglio. A big selling point was that any 9 mmP handgun could be converted to .41 AE with just a simple barrel swap.
Ballistics on the .41 AE were fairly impressive. IIRC they were somewhere between the .40 S&W and the Bren 10mm.
The .41 AE was chambered by several companies, including Desert Eagle, and I believe there was a .50 AE chambered in the Desert Eagles as well. I don't know much about the .50 AE cartridge. A quick Google search showed that the .50 AE had a rebated rim the same size as a .44 RemMag. That would allow Desert Eagle owners switch calibers by swapping barrels.
The .41 AE was a decent cartridge, I was sad to see it fail in the marketplace.
Doc