What is "Christian Apologetics"?

While discussing some of C. S. Lewis' writings (The Problem of Pain in particular), Alister McGrath gives a helpful definition of "Christian Apologetics":

The business of identifying, understanding, and answering concerns and difficulties that ordinary people have about the Christian faith, and also demonstrating its power to explain things and satisfy the deepest longings of the human heart.

–Alister McGrath, C. S. Lewis–A Life: Eccentric Genius, Reluctant Prophet, 200-01.