Imo
 

what does IMO mean? And what is a header??? I seen some headers picture but it looks like a manifold..is it another name or something??

IMO means "in my oppinion" if i'm not mistaken. as for the header you are right. usually the differences between the two is that the manigold is casted, and the header is made out of tubes and welded to flanges

IMO actually means "i masturbate often"

you do that ;) . i'll stick with in my oppinion