Short, plain definitions of the words you run into on this site, from apportionment to partisan lean. Each entry links to a fuller guide where one exists.
Congressional district
A congressional district is a geographic area within a state that elects one member of the U.S. House of Representatives. There are 435 districts, each with roughly 760,000 people. See What Is a Congressional District?
On this site: Oklahoma’s 4th district is one of the 435.
Apportionment
Apportionment is the process of dividing the 435 House seats among the states by population after each census. States with more people get more seats. See How Many Congressional Districts Are There?
On this site: California holds 52 seats and Wyoming holds 1.
Reapportionment
Reapportionment is the reallocation of House seats among the states after a new census, so the number of seats per state matches the latest population. See Redistricting vs Reapportionment
On this site: the seat counts in the full district list are the ones set after the 2020 census.
Redistricting
Redistricting is the redrawing of district boundaries within a state, usually after each census. It sets the lines that decide which voters are grouped together. See How Congressional Redistricting Works
On this site: the redistricting tracker covers the 10 states that changed maps for 2026.
Gerrymandering
Gerrymandering is drawing district lines to favor one party or group. The two common methods are packing and cracking. See What Is Gerrymandering?
On this site: the redistricting tracker records which 2026 maps were redrawn and who redrew them.
Packing
Packing is concentrating a group’s voters into as few districts as possible, so their influence is limited to those seats. See Packing and Cracking
On this site: district pages list a partisan lean, such as New York’s 15th at D+48.
Cracking
Cracking is splitting a group’s voters across many districts so they fall short of a majority in each one. See Packing and Cracking
On this site: Compare Districts puts two neighboring districts side by side.
At-large district
An at-large district covers an entire state. A state with only one House seat elects that member at large, from the whole state rather than a smaller district. See What Is an At-Large Congressional District?
On this site: Wyoming’s at-large district covers the whole state.
Incumbent
An incumbent is the person currently holding an office and running to keep it. Incumbents often have an advantage in name recognition and fundraising.
On this site: Oklahoma’s 4th district names Tom Cole as the sitting representative.
Primary election
A primary election is an early contest where a party’s voters choose the candidate who will represent the party in the general election. See How Long Is a Congressional Term, and When Are Elections?
On this site: the 2026 House elections page explains how each state picks its November candidates.
General election
The general election is the final contest, held in November of even-numbered years, where candidates from different parties face each other and voters pick the winner.
On this site: the 2026 general election falls on November 3, 2026.
Swing district
A swing district is one where either major party has a real chance of winning, based on close past results. See What Is a Swing District?
On this site: Arizona’s 6th district has a partisan lean of R+1.
Safe seat
A safe seat is a district that one party wins by a wide margin almost every election, so the result is rarely in doubt.
On this site: California’s 12th district has a partisan lean of D+74.
Census
The census is the count of the U.S. population taken every ten years. Its results drive both the apportionment of House seats and the redrawing of district lines.
On this site: district populations come from Census Bureau data, such as Pennsylvania’s 7th at 770,006 people.
House of Representatives
The House of Representatives is the larger chamber of Congress, with 435 members elected from districts for two-year terms. See House vs Senate: What’s the Difference?
On this site: browse all 435 districts.
Senate
The Senate is the smaller chamber of Congress, with 100 members, two per state, elected statewide for six-year terms. See House vs Senate: What’s the Difference?
On this site: profiles for all 100 senators.
Representative
A Representative is a member of the U.S. House who speaks for one congressional district. See What Does a U.S. Representative Do?
On this site: every district page names its member, such as Juan Ciscomani in Arizona’s 6th.
Congressional term
A congressional term is the length of time a member serves before facing reelection: two years in the House and six years in the Senate. See How Long Is a Congressional Term, and When Are Elections?
On this site: all 435 House seats are on the 2026 ballot.
Redistricting commission
A redistricting commission is a body, often independent of the legislature, that some states use to draw district lines. The goal is to reduce partisan control of the maps. See How Congressional Redistricting Works
On this site: California is one of the states that uses an independent commission.
Partisan lean
Partisan lean is a measure of how strongly a district tends to favor one party, based on past election results. A district can lean Democratic, lean Republican, or be closely divided.
To find your own district and representative, use the lookup on the home page.
On this site: each district page carries a lean from the 2024 presidential margin, such as Pennsylvania’s 7th at R+3.
Committee assignment
A committee assignment is the standing, select or joint committee a member of Congress sits on. Committees hold hearings, write bills and decide which measures reach the floor. House committee jurisdictions are set by House Rule X, Senate jurisdictions by Senate Rule XXV.
On this site: the committees of the 119th Congress, each with its full roster.