This page specifies the following tag:
This causes the following:
width=device-width: This causes the browser to match the actual device width. Rather than being
rendered at a large desktop width and scaled down. This essentially means CSS pixel sizes are accurate.
initial-scale=1: This causes the browser to start the zoom at 1. One example where this is useful:
When you rotate an iPhone to landscape orientation, by default it will zoom in on the webpage which can look
odd. Using this property keeps the zoom level the same on rotation.