Hella

Hella is an American slang term that originated in Oakland, California but has since spread to become native slang to all of the San Francisco Bay Area. It is used as an adverb such as in "hella bad" or "hella good" and was eventually added to the "Oxford English Dictionary" in 2002. It is possibly 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 since its grammatical usage does not align with those phrases. 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.
History.
Early use.
"Hella" has likely existed in California English since at least the mid-1970s. 
Geoff Nunberg, a UC Berkeley linguist, has theorised on the origins of the slang term "hella". “Hella emerged somewhere in Northern California around the late 1970s, and although it spread to other places, it’s still associated with this region,” says Nunberg. Historically, slang spreads from black English to white English and not in the other direction, which is why Nunberg says he suspects it started in Oakland, an area that, at one point, was 47% African American.
By 1993, Mary Bucholtz, a linguist at the University of California, Santa Barbara, collated materials from an urban high school (Bay City High School) in the Bay Area and found that "hella" was "used among Bay Area youth of all racial, ethnic, and socio-economic backgrounds and both genders." "Hella" remains part of the dialect of northern California, where it has grown in popularity.
Spread.
By 1997 the word had spread to hip hop culture, though it remained a primarily West Coast term. With the release of the 2001 No Doubt song "Hella Good," one Virginian transplant in California "fear[ed] the worst: nationwide acceptance of this wretched term." 
Since the early 1990s "hella" has been used regularly in the Pacific Northwest as a common slang term, particularly in Seattle and Portland, Oregon. Popular area rappers Blue Scholars and Macklemore regularly use the term in their lyrics; Macklemore uses the word several times in his worldwide hit song "Thrift Shop".
In the "South Park" episode "Spookyfish," which was the 1998 Halloween special, the character Cartman repeatedly used the term "hella" to the annoyance of the other characters, which contributed to its currency spreading nationally. "You guys are hella stupid" is one of the phrases spoken by a talking Cartman doll released in 2006. The Sacramento-based band Hella chose its name for the regional association; Zach Hill says "It's everywhere up here... We thought it was funny, and everyone says it all the time."
"Hella" was included on the BBC's list of 20 words that sum up the 2000-2009 decade, defined as "An intensive in Youthspeak, generally substituting for the word "very"".
Paralleling the use of the minced oath "heck", some people use "hecka" in place of "hella". Younger school children may be required to use this form. Church culture in Northern California also encouraged usage of "hecka" over "hella".
The Prince song "U Got The Look," released in 1987 on the album "Sign o' the Times", features the lyric "your body's hecka slammin'...", which would appear to be an early adoption of the term "hecka" in its accepted vernacular usage.
Usage.
Intensifier.
While intensifiers similar to "hella" exist in many colloquial varieties, "hella" is uncommonly flexible. It can be used to modify almost any part of speech, as shown below:
SI prefix.
An online petition begun in 2010 by Austin Sendek of Yreka, California seeks to establish "hella-" as the SI prefix for 1027. The prefix was recognized by Google in May 2010, and Wolfram Alpha in May 2011. In 2013, Andrew McAfee suggested the term "hellabyte" with this usage.