(edit for clarity)
Gerrymandering
In the process of setting electoral districts, gerrymandering is a practice that attempts to establish a political advantage for a particular party or group by manipulating geographic boundaries to create partisan, incumbent-protected districts. The resulting district is known as a gerrymander (/ˈdʒɛriˌmændər/); however, that word can also refer to the process.
Gerrymandering may be used to achieve desired electoral results for a particular party, or may be used to help or hinder a particular demographic, such as a political, racial, linguistic, religious or class group.
When used to allege that a given party is gaining disproportionate power, the term gerrymandering has negative connotations. However, a gerrymander may also be used for purposes that some perceive as positive, such as in US federal voting district boundaries that produce a majority of constituents representative of African-American or other racial minorities (these are thus called "minority-majority districts").
Read more:
http://en.wikipedia.org/wiki/Gerrymandering______________________________________________________________________________________________________________________________________
In most countries, this practice is heavily frowned upon, sometimes even illegal. It's a common practice in the US, however.