A more thorough explanation:

A congressional district is a geographical area within a state that elects one member to the United States House of Representatives. It is a political subdivision created for electoral purposes.

For example, California has 53 congressional districts, each represented by a member of the House of Representatives. These districts are created based on population and are redrawn every ten years after the census.

Congressional districts are important because they determine who represents a particular area in the federal government. The representative elected from a congressional district is responsible for representing the interests of their constituents in Congress.