NPCs are somewhat complicated beasts. In order to simplify the mental book-keeping required to handle their interactions with PCs, many games summarise their reactions to the PCs with some variously labelled statistic that essentially summarises whether they will help the PCs or if they want to do bad things to them. (Sometimes with some sort of spectrum of intermediate possiblities.)

Technically they are supposed to slide up and down this scale, depending on how the PCs treat them, but this detail is often overlooked.

Transcript

Qui-Gon: We better find shelter. Sandstorms are dangerous.
R2-D2: You're telling me...
Jar Jar: Anakin can leads us to hissa home!
GM: I'm not sure he'd take you home with him.
Qui-Gon: He's already helped Jar Jar. So he must have a positive Reaction Rating towards us. Lead on, lad!
Anakin: Uh, I guess... It's this way.
GM: He leads you to a run-down mud-brick dwelling, packed side by side with similar residences to minimise heat from the harsh rays of the desert suns.
Qui-Gon: Inside, quick, before we start taking damage!
Jar Jar: Wesa made it!
Qui-Gon: Mmm. Perfect disguise for a mob den. I search for blasters.
R2-D2: {muttering to self} Book of Giant Sand Creatures, and all he can roll up is a bleep boodle boop sandstorm...
Qui-Gon: Hey, we got XP for that encounter, right?