It is important to clarify from the outset that the string is not a standard or manufacturer-released filename for any mainstream network operating system. At first glance, it resembles naming conventions used by Cisco IOS (Internetwork Operating System) or IOS-XE for virtual or embedded platforms, with heavy modifications.
Below is a conceptual "white paper" outline regarding this specific type of image, its technical context, and its use in modern networking labs. i86bilinuxl3adventerprisek9m21573may2018bin portable
Designed to run natively on a Linux kernel rather than standard Cisco proprietary hardware. It is important to clarify from the outset
Summary
Because this is an adventerprisek9 image, it does not cut corners on enterprise software capabilities. Engineers have access to: its technical context