viewport

A viewport is the portion of a display or document that is visible at any given time. In computing, it refers to the area of the screen, window, or canvas where content is drawn and can be seen by the user. The term contrasts with off-screen content that is not currently rendered.

In web design, the viewport is the area of the browser window through which a web page is viewed. On mobile devices, the size of the viewport can differ from the device’s screen size, so responsive design uses the meta viewport element, CSS units like vw and vh, and media queries to adapt layout.

In computer graphics and game development, the viewport defines the rectangle in the render target into which the final image is rasterized. It maps the pipeline's normalized device coordinates to screen coordinates and influences rendering resolution and aspect ratio. The term is often used together with the view frustum, camera, and field of view.

In geographic information systems and computer-aided design, a viewport is a window into a larger dataset or model space. It specifies the geographic extent or portion of the model being displayed, potentially with its own scale and coordinate reference.

Viewport changes can occur due to window resizing, device rotation, or user zoom. Modern applications manage viewports to optimize performance through culling, tiling, or level-of-detail strategies, and to ensure content remains legible across devices.