“Always be prepared to make a defense (apologia) to any one who calls you to account for the hope that is in you, yet do it with gentleness and reverence…” (1 Peter 3:15)
Apologetics is the theological science by which one is ready to give such a defense. It can be the well-studied efforts of an "apologist," or those of an ordinary Catholic who loves the Lord and rushes to defend the truth. It is typically the case, that such as a defense is necessary in order to defend against false accusations, rather than simply to explain the faith. The latter is more properly the discipline of dogmatic theology. However, the two are closely allied, the former leading to belief by overcoming obstacles to it; the latter leading to a deeper penetration and understanding of the faith already held.