[steam + punk]
neologism : a sub-genre of speculative science fiction
set in an anachronistic 19th century society

"There is a new genre climbing to popularity within
the science fiction world of writing: steampunk. A
mix of Victorian times and futuristic [steam] machines
clash to create a unique world.."

I try to find the meaning of 'speculative' in this context.
Even if I were a true born native speaker I'm afraid I would not understand.