Chronic is the general term for marijuana.

Kush refers to a kind of Indica Strain (body high, mellow and very relaxing).  Excellent for pain control , anxiety/stress and insomnia). It has a pungent sweet smell.  Examples are White Widow, Northern Lights, OG Kush, Purple Kush. Often it is a hybrid but mostly Indica.  Greener than Sativa or purple. Maximum indoor plants come from Indica.