Hum- I'm new to this whole MMO slang thing. What IS Quest Chaining?

(also, nowadays when I think 'open world content' I remember of my playthrough of Dragon Age 1... The final battle... It must have been friggen epic, except I never saw it, had to play with the camera facing outward/the sky and get as little as possible of the battle on my screen at any time, otherwise the game would crash )