Using SVGs for Resolution Independence
Entire books have, are being, and will be, written about SVG (an abbreviation for Scalable Vector Graphics). SVG is an important technology for responsive web design as it provides pin-sharp and future-proof graphical assets for all screen resolutions.
Images on the web, with formats such as JPEG, GIF, or PNG, have their visual data saved as set pixels. If you save a graphic in any of those formats with a set width and height and zoom the image to twice its original size or more, their limitations can be easily exposed.
Here's a screen grab of just that; a PNG image I've zoomed into in the browser: