I see some engines on evil-bay for sale, some say they are a long block. What makes the engine a long block? and what makes them a short block.

Long block = Block with heads. P/C's etc.
Short Block = Block P'C's but no heads.

Let me start off by saying that "I'm probably wrong"
but I thought a long block was when it was complete, from carb to oil pan (like an SBC)
and a short block was when it was relatively incomplete, like missing the intake, heads, or etc etc.

If I'm right then

if not then

to me

That was fun, can I do it again?

The usual terminology is thus:

Short block usually means cases and everything inside the cases (crank, cam, lifters). This may or may not include barrels.

Long block means a short block with barrels and heads. For the Type IV, this might include the fan housing and fan, but often won't. No intake system, usually. Rarely any tin. Take a dead engine and a long block and you have a complete, running engine.

A "complete" or "dressed" engine is usually more or less as it's pulled from the car. Includes intake, alternator, tin, sometimes exhaust.

The exact definitions vary from person to person and engine type to engine type. For most water-cooled engines, for example, the short block will often be the block, crank, rods, pistons. No head, water pump, alternator, etc. A long block would be a short block with a head, and often a water pump.