There are interesting terms in Trainz:
-kuid (what the heck is this?)
-Spline (why are some objects called "splines"?)
-ATLS (I pronounce it "Atlas")
-Boat'z (something to do with add-ons???)
-trackmark
-Content Manager
-Autosave (sometimes saving or overwriting a Route/Session generates an "Autosave" version involuntarily)
-Surveyor (a virtual world where train layouts and operating behaviors are built, polluted [correction, I meant POPULATED] with objects or modified)
-Assets (like "liquid assets" in accounting??)
KUID is a unique identifier for an asset (object) in Trainz that identifies both the author, the asset and the version number. I think KUID is short for Kool Unique Identifier but I could be wrong.
Spline (look up Google for this but fundamentally it is an asset that can stretch to be one or more copies of the same asset). Just to muddy the waters, spline is not a spline any more but is now a track. See below.
For ATLS and Boatz see
http://www.boatztrainz.co.uk/atls.html Using ATLS is rather difficult so you might want to set that one aside until you get more familiar with Trainz.
Trackmark is a track mark (duh!). Literally, it is a marker you can add at a track location for various uses.
Content manager manages content (another duh!). You can create new content, get new content, find new content, etc. The Content Manager in Trainz:A New Era looks radically different from TS12 Content Manager so that might confuse.
Autosave supposedly automatically saves a copy of your route/session at regular intervals. I've never found it useful.
Surveyor is the world where you create a new track and session. Why it's not called "Route Builder" or something similar beggars belief. Perhaps someone else used that name before (MSTS?).
Assets? Well, just a name for something you have or don't have so I guess asset is as good as anything. Some of us don't have any liquid assets and are just poor old pensioners.
There are plenty of other weird names in Trainz. You can have a track asset which is not a track at all but looks like a bridge or a fence or a row of telegraph poles or even a row of cows. But not let's get picky.
See also
https://en.wikibooks.org/wiki/Trainz