In the United States, every state elects a certain number of people to service in the House of Representatives. The exact number is based on the census count of the State's population. The process of determining who exactly is in each district, however, is up to the states. Pennsylvania, for example, has 18 House reps, so Pennsylvania has to be divided into 18 congressional districts with roughly the same population of 700,000.
In most states, the process of mapping the Congressional districts is controlled by the majority party in the state legislature. And sometimes (often) this conflict of interest gets the better of them, and the result is giant disgusting gerrymanderers!
Gerrymandering is when the map-drawing process is intentionally used to benefit a particular party, either to help win more seats in the legislature or to protect the one it has.
The goal is to draw many districts that will elect members of the same party and only a few that will elect members of the opposite party.
It kinda is, but it probably shouldn't be since it clearly alters the democratic process. In fact, an important decision about gerrymandering's legality is now in the hands of the Supreme Court, which heard Gill v. Whitford in September and will rule on it in the spring. The case is about whether the very northern middle-y state of Wisconsin's redrawn legislative map is an example of partisan gerrymandering, and whether that's legal. Find out more here!