A word widely used by the youth of the Sanfrancisco Bay Area and it's surrounding cities. It can be used as an adjective, noun, adverb, and a few interjections, but it is mostly used as an adverb. It can replace descriptive words meaning "high quantities", primarily words such as 'very' and 'many', and also substitutes for words groups like 'a lot' and 'a bunch'
very- He was going hella fast.
many- Hella people died that day.
a lot(of)- I had hella fun, but I gtg now.
a bunch(of)- He pwned hella n00bs last game.