Understanding Viewports and Devices

Leave one particular line of HTML out of a page, and a phone lays the page out as if its screen were 980 pixels wide. It then shrinks the whole result to fit the real screen, so 16-pixel text appears about 6 pixels tall. That line is the viewport meta tag, and every responsive page needs it.

What Is a Viewport?

The rectangle of the browser in which the page is drawn is called the viewport. On a laptop it is the browser window, minus the toolbars, so it changes size when you resize the window