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:

Can you see how the image looks obviously pixelated? Here is the exact same image saved as a vector image, in SVG format, and zoomed to a similar level:

Hopefully the difference is obvious.
Beyond the smallest graphical assets, where at all possible, using SVG rather than JPEG, GIF, or PNG will produce resolution independent graphics that require far smaller file sizes compared to bitmap images.
While we will touch upon many aspects of SVG in this chapter, the focus will be on how to integrate them into your workflow, while also providing an overview of what is possible with SVG.
In this chapter we will cover:
img and object tagsSVG is a dense subject. Which portions of this chapter are most relevant to your needs will depend on what you actually need from SVG. Hopefully, I can offer a few shortcuts right up front.
If you simply want to replace static graphical assets on a website with SVG versions, for sharper images and/or smaller file sizes, then look at the shorter sections on using SVG as background images and within img tags.
If you're curious about what applications and services can help you generate and manage SVG assets, skip down to the section, Creating SVGs with popular image editing packages and services, for some useful links and pointers.
If you want to understand SVG more fully, or animate and manipulate SVG, you had better get yourself comfy and get a double size of your favorite beverage as this is quite a long one.
To begin our journey of understanding, step with me back into 2001.
The first release of SVG was in 2001. That was not a typo. SVG has been 'a thing' since 2001. While it gained traction along the way, it's only since the advent of high-resolution devices that they have received widespread interest and adoption. Here is the introduction to SVGs from the 1.1 specification (http://www.w3.org/TR/SVG11/intro.html):
SVG is a language for describing two-dimensional graphics in XML [XML10]. SVG allows for three types of graphic objects: vector graphic shapes (for example, paths consisting of straight lines and curves), images, and text.
As the name implies, SVGs allow two-dimensional images to be described in code as vector points. This makes them a great candidate for icons, line drawings, and charts.
As vectors describe relative points, they can scale to any size, without loss of fidelity. Furthermore, in terms of data, as SVG are described as vector points, it tends to make them tiny, compared to a comparably sized JPEG, GIF, or PNG file.
Browser support for SVG is now also very good. Android 2.3 and above, and Internet Explorer 9 and above, support them (http://caniuse.com/#search=svg).