[The Saucepan Man]

It is generally accepted that Orcs and Goblins are one and the same race, and all the textual evidence points that way, as has been noted in this thread already.

I do, however, still picture Goblins as a particular type of Orc - smaller and better suited to living communally in caves and tunnels - because that is the way that I imagined them when I first read the books.

And I see no reason why Orcs should not come in all shapes and sizes. I rather liked that aspect of the films - the portrayal of different Orc types, and particularly the differentation between the Orcs of Moria with their large cat-like eyes (better suited to darkness?) and the larger fighting Orcs of Mordor and Isengard.

Uruk Hai are also a particular type of Orc (Uruk means Orc), bred (first by Sauron, not Saruman) for strength, aggression and resistance to sunlight, as the piece from the Encyclopaedia of Arda quoted above indicates.

Half-Orcs and Goblin-Men are mentioned, I think, only in reference to the Army of Isengard and it is to be presumed that they were the result of cross-breeding between Men and Orcs by Saruman. Whether there was a difference between the two is not clear, although the use of two different terms might suggest that there was.