Hella is an American slang term that originated in the San Francisco Bay Area, but has since spread to become native slang to all of Northern California. It is used to describe such as 'hella bad' or 'hella good', and eventually added to the Oxford English Dictionary in 2002. It is probably a contraction of the phrase "hell of a" or "hell of a lot [of]", in turn reduced to "hell of", though some scholars doubt this etymology.[1] It often appears in place of the words "really," "a lot," "totally," "very" and in some cases "yes". Whereas hell of a is generally used with a noun, according to linguist Pamela Munro, hella is primarily used to modify an adjective such as "good."

According to lexicographer Allan A. Metcalf, the word is a marker of Northern California dialect. According to Colleen Cotter, "Southern Californians know the term ... but rarely use it." Sometimes the term grippa is used to mock "NorCal" dialect, with the actual meaning being the opposite of hella.

Source: https://en.wikipedia.org/wiki/Hella