I believe it stands for "viewport width" which is specified in percents over the width of the browser viewport. Google has a first-class definition, too: https

I believe it stands for "viewport width" which is specified in percents over the width of the browser viewport. Google has a first-class definition, too: https://www.google.com/search?q=css+vw+unit https://www.google.com/search?q=css+vw+unit