This specific string, , is a filename for a Cisco IOS software image. Specifically, it is a Cisco IOL (IOS on Linux) binary used primarily in network simulation environments like EVE-NG , GNS3 , or PNETLab .
Indicates this is a 32-bit binary designed to run on Intel x86 architecture. i86bilinuxl3adventerprisek9m21573may2018bin
The standard file extension for a binary executable file. Why Use IOL Instead of VIRL or Dynamips? This specific string, , is a filename for