Does this mean the same thing to everyone?

Usually it means the engine was rebuilt without removing the block from the frame; very common, since the block does NOT get rebored, but gets new sleeves instead. there is usually no need for any machining on the block on the first or second overhaul, so it is done "in-frame".
Does this clarify things for you?

Somewhat.

More specifically what is typically included with an in-frame rebuild besides the sleeves and I assume the pistons?

By convention does that definitely include a list of things?

Does the term "overhaul" mean anything different?

Often used HD trucks will note X miles since in-frame "rebuild" or "overhaul".
I'm just trying to read between the lines of these ads to compare apples to apples.

USUALLY it includes the mentioned sleeves AND pistons and rings, plus main and rod bearings(yes, they CAN be changed with the crank in place). Plus the head(s) are usually gone through as long as they are off. This includes checking out the fuel injectors if necessary.
So all in all, an inframe can be fairly comprehensive. Usually the only time an out-of-frame is done is if there is block damage or very severe wear, where EVERYTHING should be thoroughly disassembled and checked out.
I hope this helped you!

That was helpful.
Forgive the simple questions.

A related engine testing question for the diesel mechanics on this informative forum:

What is blow-by?
How do you measure it?
What is a tolerable amount on a used engine? (How much blow by does a new engine have straight out of the factory? After in-frame rebuild?)
Is this an essential part of the used truck inspection before purchase?

Blow-by is the gasses that escape past the rings in a worn engine. A new OR overhauled engine will have next to no blow-by, because the rings, pistons, and cylinders are all new either way. The way you measure it is by observing how much blows out the crankcase breather tube. A new engine will have next to none, if any. And yes, you DO want to check this on anything you want to buy. Does this help you?

Very much. Thank you.
How important is Dyno testing and what does that entail?
If the Seller has not had these tests done, is it fair to ask him to do them?

When I bought the last group of trucks for my business, I got the Peterbilt dealer to go over the overheads and to put them all on the dyno. They did this in part because I wanted to make sure as used trucks that they were up to spec's. The other reason was to get the 1 yr 100,000 mile warranty from Detroit. The trucks had just over 500,000 miles on them. All had some blow by. One of the four had some issues when they ran the overhead and they had to spend about $1800.00 to get it right. One when it was dyno'd was lacking horsepower and they had to take care of that. So it is fair to ask the owner to have it checked but they may tell you to pay for it. Some of my trucks with 700,000 miles on them have a lot of blow by but I am still running them. One of them under 200,000 has visible blow by. Blow by itself is not a big deal unless it is enough to be dumping oil all over the place. Look good under the truck at he places that are not easy to steam clean and see if there is alot of oily debis and that will tell you if you should have it checked out. We used to have some older detroit engines that leaked about a gallon of oil a day thru the blow by and that was considered average!!

Wick