Chronic is weed. It's just good weed. First you have you Regs which is regular weed. Then you have Chronic which is good weed. Then you have your Kush which is really good weed. There are a lot of different types of Chronic and Kush though. Ex Chronic: Northern lights,White widow,White Rhyno and much more Ex Kush:Purple Kush,Bubba Kush,Ak 47 and much more
Chronic will lay you down after 3 hits. Weed just makes you feel good for an hour or so.
Vernacularly it's the same thing. It depends where you are and who you encounter on whether someone will call it weed, chronic, refer, green, trees, bud etc etc etc...