Native resolution is the actual number of pixels your screen can display horizontally and vertically. It's a fixed specification set during manufacture, not something you can change. A 1440p monitor, for example, has a native resolution of 2560 by 1440 pixels.
When a game or video runs at your display's native resolution, each pixel on screen represents exactly one pixel of image data. The result is the sharpest, clearest picture possible. If the source content is at a lower resolution, your monitor must upscale (enlarge) it, which softens the image. If content exceeds native resolution, your GPU must downscale (shrink) it, adding processing overhead.
In gaming, matching your game's resolution to your monitor's native resolution is the best way to get the visual quality and performance your hardware can deliver. For example, running a game at 1440p on a 1440p monitor will look noticeably crisper than running it at 1080p, even if your frame rate is slightly lower. Conversely, running at a lower resolution on a high-resolution display can introduce blurriness or pixelation unless the game applies anti-aliasing or other smoothing techniques.
When shopping for a gaming monitor, native resolution is one of your key buying criteria. Higher resolutions (like 1440p or 4K) demand more from your graphics card, so consider both your monitor choice and your GPU's ability to drive it. Check your monitor's specs sheet for the listed resolution; this is always the native resolution, not a refresh rate or any other figure.