A viewer is someone who watches something, whether it's a television show, a movie, a video online, or even a painting in a museum. When you sit down to watch your favorite show, you become a viewer of that program.

The word emphasizes the act of looking and watching rather than listening or participating. Television networks care deeply about their viewers because those are the people actually watching their shows. A YouTube creator checks how many viewers watched their latest video. Museums want viewers to appreciate the art on display.

You can also use viewer for devices that help you see things, like a slide viewer that lets you look at old photographs. In this sense, it's a tool for viewing rather than a person.

Unlike words like “audience” (which can include listeners at a concert), viewer specifically refers to someone using their eyes to watch or observe. When a nature documentary narrator says “viewers at home,” they're talking to everyone watching their screen at that moment, which could be millions of people around the world.