Type Tips – Ligatures

From FontShop founder Erik Spiekermann

A ligature is defined as the visual or formal combination of two or three letters into a single character. They consist of letter combinations such as ff, fi, fl, ffi. Ligatures keep letters from overlapping and improve legibility. For example: affluence, configure, deflate, affinity.

For more info on ligatures, kerning and tracking the Design Center has a pretty good article posted.