SVG (Scalable Vector Graphics) is an XML-based vector image format. SVG has several potential benefits over other graphics formats like JPG or PNG.
Firstly there's a clue in the name - SVGs are scalable - they can be resized when viewed with no loss in quality or pixelation like you might get with a JPG or PNG.
Further, you'll often find that for logos and simple graphics SVG images can be smaller in file size too - which means your website will load quicker - double win!