What It Is:
Funk is a very distinct style of music based on R&B that reached its height in popularity from the late 1960s to late 1970s. Its name originated in the 1950s, when "funk" and "funky" were used increasingly as adjectives in the context of soul music -- the meaning being transformed from the original one of a pungent odor to a re-defined meaning of a strong, distinctive groove. One of the most distinctive features of funk music is the role played by bass guitar.
The Importance of Bass:
Before soul music, bass was rarely prominent in popular music. Players like the legendary Motown bassist James Jamerson brought bass to the forefront, and funk built on that foundation, with melodic basslines often being the centerpiece of songs. Other noteworthy funk bassists include Bootsy Collins and Larry Graham of Sly & the Family Stone. Graham is often credited with inventing the "slap bass technique," which was further developed by later bassists and became a distictive element of funk.
What Makes It Distinct:
The stong bassline is primarily what separates Funk from R&B, soul and other forms of music. Melodic basslines often being the centerpiece of songs. Also, compared to the soul music of 1960s, funk typically uses more complex rhythms, while song structures are usually simpler. Often, the structure of a funk song consists of just one or two riffs. The soul dance music of its day, the basic idea of funk was to create as intense a groove as possible.
The Funk genre has lost most of its popularity since the 1970s, but saw a mini-revival in the early 1990s due to the sampling of Funk songs by hip-hop artists. Examples of popular contemporary funk artists include Soulive and funk pioneer George Clinton, who's still recording new music after more than three decades. Also, many rock bands use a stong funk element in their music, including Primus and the Red Hot Chili Peppers.