On Mon, 13 Jun 2016 19:37:44 +0000, Noel Torres wrote:
> Hi folks...
>
> Where can I find a *good* and *deep enough* explanation of what a
> "shim" is

https://en.wikipedia.org/wiki/Shim_%28computing%29

In short: A shim is an adaptation or compatibility layer
that enables software to use functionalities of other
components not actually present on the system (or present,
but in an older version, or the like). It does so by
providing the desired functionality itself, or mapping it
to other third party libraries, or simply by faking it.

A typical example would be a "thin" wrapper library that
maps one API (-version) onto another API (-version).

(In technical engineering context, a shim is generally
some kind of lining plate or metal spacer (e.g. a simple
washer) used to mechanically adapt pieces of machinery or
equipment.)

> (in the context of systemd and EFI),

The systemd-shim package in debian allows software to use
systemd functionality without the need of actually having
systemd installed and running as PID1 on the system.

Not sure about the (U)EFI context. I assume it would be a
signed bootloader that allows some kind of chain-loading
other arbitrary (unsigned) OS kernels.

> but also *easy enough*
> to explain it to some colleagues at work?

That would depend on where you work, and how well educated
your coworkers are. ;-D

HTH, Regards
Urban