It is you, if you live in a representative's district. The whole machinery of representative government rests on the relationship between an official and the constituents they answer to.
A constituent is a person represented by an elected official, typically a resident of that official's district or state. The word shares a root with constitute: constituents are the people who, together, make up the body an official represents.
The relationship is the basis of representative democracy. A representative is supposed to serve, listen to, and answer to their constituents. Constituents, in turn, hold the ultimate power: they can vote the representative out.
Serving constituents is much of what elected officials actually do. Beyond passing laws, their offices handle constituent services, helping individual people navigate the government, chase a lost benefit, or cut through bureaucracy. It is retail democracy, one citizen at a time.
The word also carries a warning about loyalty. An official torn between their constituents, their party, their donors, and their own conscience faces the defining tension of the job: whose interest comes first when they conflict?