dual core, core duo, core 2 duo, quad core  

You should probably google them for specifics but all i know is that dual core and core 2 duo are two processors working in tandem and quad core is 4 processors working in tandem. This enable users to do multi-tasks.

To make it more understand and short, the only difference is the speed- how fast it will be processing and usage... dual core is already phased out...

for consumers like us who will surf the net or using basic needs, core 2 duo (2x speed) is enough... as for the quadcore which is 4 x the speed is using for servers, gaming, doing video editing, or any large multimedia designs... for me, im using the first quadcore ... so i won't keep upgrading my parts in d future. =) hope it helps.