Gerrymandering: 1. to divide (a territorial unit) into election districts to give one political party an electoral majority in a large number of districts while concentrating the voting strength of the opposition in as few districts as possible
2 : to divide (an area) into political units to give special advantages to one group.
Source: http://www.merriam-webster.com/dictionary/gerrymandering

Both democrats and republicans are guilty of this insidious practice. Just as the definition describes, it allows politicians to retain power by annexing certain populations into their district who tend to vote in their favor. With a practice known as “packing and cracking”, politicians are able to ‘pack’ in extra votes in their favor to offset votes that might be against them in their district by ‘cracking’ neighboring districts. In addition, these votes are typically taken away from districts where the controlling party has no material chance to win. This allows them to take what would otherwise be “ineffective” votes and include them in their own district to have the maximum effect on their re-election.