Terrain question

Hi, I am reading the book opengl game programming and i am playing with the code of chapter 8/10 (Textured heightfield terrain). I have a question about texturing the terrain. The code from the book uses one (grass) texture and put this texture on every quadrilateral. So in fact they use 1 texture and place let say 2000 times and the terrain is filled with green grass. I downloaded some other terrain demo''s and they all used ONE texture to cover ALL of the terrain, not putting the texture on ONE quadrilateral. They some howe broke up the texture in pieces that fit on one quadrilateral. I hope i make any sense Can some explain to me how they can use one texture to cover all of the terrain or even better some code. Thanks BoldyMan