One of the major differences between face-to-face roleplaying and computer roleplaying is that when you are speaking to real people you can say anything at all (that makes sense in your language) and be understood. Computer games still struggle to interpret the full complexity of natural language. The stop-gap solution in early computer RPGs* was to offer the player a selection of pre-canned dialogue snippets that they could choose from. The computer character's response could then be controlled to a small, finite** number of possibilities, from which further canned possibilities were offered to the player, leading to other computer responses, and so on. The resulting branching structure of the potential conversations is called a dialogue tree.
* Where "early" means any computer RPGs without some sort of arbitrary natural language parsing capability. Which is still almost all of them. (Text adventures don't count.)
** It's an oddity of natural language that the adjective "small" applied to the noun "number" should make the additional adjective "finite" entirely redundant***, yet somehow leaving out the "finite" feels like it's understating the point too much.
*** Okay, not entirely redundant, for the mathematics nerds who know about different classes of infinities.
C-3PO: I'm quite sure you'll be very pleased with that one, sir.
R2-D2: Thank you, Threepio. I just want to say sorry about—
[SFX]: < doop oobloo pating doip bloop >
C-3PO: He's very obedient. And tactful.
Adam: So he's playing someone completely different from himself? This roleplaying stuff is insane.
C-3PO: Tell us something about yourself, Adam.
Adam: Um... I've been living on this farm all my life.
C-3PO: Go on.
GM: You can invent some stuff about yourself.
Adam: And... er... I'm an expert crack-shot ninja karate master stunt driver with a suit of powered armour?
GM: Spoken like a true relative of Pete. Keep it within reason for a desert farm boy.
Adam: Ummm. Um. I like... sand.
Adam: I can... drive a sand tractor?
Adam: Wow. This is so much harder without a dialogue tree.