a relatively small gang based in Lansing, Michigan; essentially, the Lansing small-town-version of the Mexican Mafia.

It is not a serious crime syndicate ((such as the Italian Mafia or Russian Bratva, LA-based gangs ("Crips" and "Bloods"), AVLN ("Vice Lords"), of Hong-Kong Triad Society)), but rather a small group of masquerading emulators known (and often prosecuted) for distribution of controlled substances, especially Marijuana.

the name is not five-hundred-seventeen, but rather five-one-seven, and is derived from the telephone area code for Lansing/Mid-Michigan.
the other day on my way home, i saw 3 mitsubishis pull up and about 20 asian mafia dudes jump out and whoop the ungodly fuck out of these 2 kids from the 517.
by Wild Drunken Bill September 4, 2007
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F*** man! I just went 517
by Grant February 19, 2004
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crunk ass, hard ass, thug ass, rappers reppin' da 507 that like to beat da koot. pussy fart causin' nukka's.
girl 1 "those 517 kings made my pussy fart last night."
girl 2 "they got you too?"
by east street September 20, 2009
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