A typeface is a group of symbols destined to be rendered as words. The purpose of all letters is to communicate a visual or linguistic message to you, the reader. Sometimes they tell a story in a novel, sometimes the news of the day. At times, they direct you on the highway, while other times they update you on what your friends are having for dinner.
A typeface is a bunch of drawings that come to life when used as text. The words and their context will differ, and, therefore, the function of the typeface will vary according to the intended usage. A typeface designed to shout news headlines at people rushing about to get to work will be different from a typeface designed to capture the delicacy of a French wine.