Screen resolution refers to the total number of pixels that can be displayed on a screen, typically expressed as width × height (e.g., 1920×1080).

Viewport size is the visible area of a web page within the browser window, measured in CSS pixels.

Device Pixel Ratio (DPR) is the ratio between physical pixels and CSS pixels, used to support high-resolution (Retina) displays.

Understanding screen sizes, resolutions, and DPR helps developers create responsive websites that look great on all devices. It's essential for optimizing user experience across different screens.

It's good practice to check device information when testing responsive designs, debugging display issues, or ensuring your website works correctly across different devices and browsers.