here's what I know:

spliff=joint=J. it is a cigarette-style way to smoke weed. it may or may not have tobacco in it, it is still the same thing. (is a piano with a cat inside suddenly a computer? no. it is still a piano, albeit a noisy one). if you have to keep lighting it, slap the person who rolled it every time you have to spark the lighter...or get non-damp weed. mixing tobacco into the joint can help with this, try it with about 1/2" of the end of a cigarette...you barely notice, especially if you already smoke cigs.

a blunt is a larger version of a joint, although joints can be bigger than blunts sometimes. a blunt is called a blunt because it has a dark, tobacco wrap instead of rolling papers. 'philly' is the term for the original cigar used to make blunts, it was a philadelphia(sp?) brand cigar that was most easily cut open and emptied; it left a nice flat paper, perfect for rolling, and it had a removable band that could be used to hold the finished blunt together.

soapbar hash = a generally bad idea...you don't know what's been mixed into it, you don't know who made it, you don't know how old it is etc. it will get you high, but your money is better spent elsewhere, like on weed maybe.

smoking a cig after smoking weed is fairly common practice as far as I know...'aftertoke smoke' is the best term I can think of, and in my experience, it does get you higher. I don't think I can say the same for weed mixed with tobacco, although the taste is more noticeable with a bowl, especially if you're smoking a roach.

a roach = the last little bit of the joint/blunt, which should be sticky with resin and very very smelly...but also very potent. if there's tobacco in it, it will taste horrible, plain and simple.