Does dual core mean double the speed?

[BrandiDup]

I'm not good with all of the computer hardware stuff but since I've had this laptop, I was always under the impression that it was 1.73 ghz b/c thats what it is, but last night my husband told me that the dual core means it's basically 1.73 x's 2. I don't really understand the reason behind having a dual core instead of just 1 core (is there such a thing? ). What is the reason behind a dual core versus just a regular computer that's super fast or something?