Typography

Typography is the craft of arranging text, including the choice of typeface, the size, the spacing and the line length, so that it is easy and pleasant to read. Good typography is usually invisible: you simply glide through the words without noticing the effort behind them.

It is like the difference between a clearly printed menu and a cramped, faint one that makes you squint. Typography matters because most of the web is words, and text that is comfortable to read keeps people on the page, while poor spacing or tiny type quietly drives them away.