No , Poetry is the overarching field - Slam poetry is that area of the field written for Poetry slams
Yes, slam poetry is performed on a stage, by pretentious, 'hip & trendy' twenty-somethings who use verse to portray their cool 'urban' lifestyles, and is watched by equally pretentious twenty-somethings who will whoop and cheer and applaud noisily with their hands raised above their heads at the end of the reading (and sometimes during if the reader throws in a swear word).
Couldn't the same be asked about the Jacket Potato and the generic Potato? I find these styles of writing (not the potatoes, I mean) tend to just be a representation of the times, and how they change according to the latest "trend". However, I mostly agree with OurJud:
To give a bit more of a neutral stance -though I agree with Jud in principle- Slam is mostly improv; they make it up on the spot. Written poetry pays careful attention to the use of language, and since you have time, you can better craft your work.
I don't know. I've been to some slams and all that stuff sounded pretty polished and rehearsed to me.
Yes. I could be wrong, but I think @OJB may be incorrect. I'm pretty sure it's not made up on the spot.
I've not gone to one since I was in my early 20s, (I might have even been 19 at the time.) But If I remember the two time I went, there was a musical beat that was picked by random by the D.J, the subject/theme was not known until the event. It was like a cross between a rap battle and a poetry-reading.