What would you call this bike? Not anything like a track bike. Not a fixed gear. Not really a conventional "road bike", if there is such a thing as a conventional SS road bike... it's currently under construction as a replacement for my other mongrel SS.

Redline 925 frame
lightweight 700c road wheelset (cassette freehub) with spacers and a single cog, 25c tires
Shimano LX (MTB) crankset with 44T big ring
front and rear brakes
MTB low-rise handlebar with bar tape

Is there some kind of common bike shop guy term for this kind of cross-breed bike?

Frankenbike

car

Well I think that sums it up pretty well... but also describes all of my bikes!!

That's a perfectly reasonable SS, perhaps a commuter bike. I don't see why one wd use a freehub but then it will work just fine so who cares.

You'll have some spacing issues using a freehub on that 120mm frame, but it's steel and you can squeeze it in there. Other than that, doesn't sound too unique, really.

I've heard them called "Frankenbikes" or "Frankenstein Bikes".

Similar to a "Frankenstein Guitar" - a guitar made of mis-matched components.

Here's an example: Eddie VanHalen's "Frankenstrat" (Fender Stratocaster)

https://www.evhgear.com/frankenstein/

Well I guess since I won't commute on it, I wouldn't think of it as a commuter bike.

I kind of was on the fence about the wheels and hub but I picked the freehub wheel mostly because it eases chain line problems with a MTB crankset, and regular standard road wheel sets with cassette hubs are far less expensive and lighter weight compared with dedicated SS wheels. Likewise it is much easier to work out gearing and even allows me to run a couple of cogs easily for gear changes without flipping the wheel. You can buy several cassette cogs for the cost of one freewheel. Seems to me track hubs only really make sense if you are going to run FG, and I am not. So in the end, the cassette freehub road wheelset just made a lot more sense for my application.

That's the nice thing about just whipping up what you need from scratch. You get just what you need and don't have to conform to anybody else's idea of what's right.

singlespeed roadbike.

i think for it to technically qualify as a frankenbike it needs a banana seat.

Done to death.