What exactly is a semi-truck?

In my spare time I like to cruise You Tube and watch dash camera videos. I find this interesting and instructive. However, without fail, every singe video I’ve seen always referred to 18 wheelers as semis. I remember reading years ago that this is not correct; that a semi is technically a truck wherein the 1st cargo area is physically attached to the frame, along with the cab. Where it’s not, it is called a tractor and trailer(s). Can any OTR truckers enlighten me?

“Semi” refers to the trailer, actually:

" A semi-tractor-trailer truck , also known as simply a semi-trailer truck , semi-tractor truck , semi-tractor-trailer or tractor-trailer truck , is the combination of a tractor unit and one semi-trailer or more to carry freight. A semi-trailer attaches to the tractor with a type of hitch called a fifth-wheel.

It is variously known as a transport truck, semi-truck, trailer truck, tractor truck, transfer truck, articulated truck, articulated lorry (UK), artic, single truck, semi-trailer, tractor-trailer, semi-tractor, semi, trailer, tractor, big rig, eighteen-wheeler, depending on the country and region."


A semi truck is just one little modification away from a fully truck…


As a retired OTR driver I can say both definetions you have are correct an are used for the same thing the most common usage is semi 18 wheeler or tractor trailer in that order technically semi means half in this case you need both halfs to do the job which is moving a load from point A to point B.

It is called a semi because the trailer is a semi trailer. a full trailer would have wheels at both ends and a tongue like a child’s wagon. An 18 wheeler is the most common form with 8 wheels on the rear of the tractor and 8 wheels on the back of the trailer but there are other configurations. When I drove thruway tandems on the NY Thruway and Mass Pike. I was usually driving a 34 wheeler, however sometimes a tandem dolly (8 wheels was not available so had to use a single dolly (4 wheels).

I preferred the superior tracking of the 8 wheel dolly.

When I pulled 3 short trailers in Ohio, I was driving a 30 wheeler.


Yep, anything with a tractor and trailer and anything else wa a “Short Job”


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I would like to thank all of you for your responses. I’m the sort that kind of cringes when words are used incorrectly and this has always annoyed me somewhat. It’s good to lose this particular nit to pick.

[quote=“Dakotaboy, post:7, topic:179489”]
I’m the sort that kind of cringes when words are used incorrectly and this has always annoyed me somewhat.

The two words that always bugged me was one that I don’t think is used any more was a cordless scew driver as I don’t ever remember seeing one with a cord the other one is Bobcat which is a brand only of a skid steer loader.


Remember a used car dealer advertising every car comes with a cordless cigarette lighter :slight_smile:

Never heard that one before.

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A dremel tool with a screw driver bit? :laughing:

What about “Crescent Wrench”, “Vise Grips”, or “Channellock” ?




True and I know there are quite a few others I can’t think of right off hand. By the way I didn’t mean to hijack Dakotaboy’s post when I said that sorry Dakotaboy.

Hand and arm power?. :laughing:

Still not sure the difference between a stillson and monkey wrench, though I call them pipe wrenches.



A trademark for a monkey wrench having serrated jaws that tighten as pressure is applied to the handle.
The Stillson name is that of the original patent holder


Probably a Zippo. Unless it also came with high compression battery cables and self-lubricating muffler bearings.

Bobcat seems to be the brand of skid steer most popularly used around here, for reasons Dad and I can’t quite understand my Mom has wanted to drive one badly.