Apologetics - being able to give an explanation on why you
believe.
But in your hearts set apart Christ as Lord. Always
be prepared to give an answer to everyone who asks you to give the
reason for the hope that you have. But do this with gentleness and
respect, keeping a clear conscience, so that those who speak maliciously
against your good behavior in Christ may be ashamed of their slander.
1 Peter 3:15-16 (NIV).
Apologetics is the field of study concerned with the systematic
defense of a position. Someone who engages in apologetics is called
an apologist. The term comes from the Greek word apologia,
meaning the defense of a position against an attack, not from the
English word apology, which is exclusively understood as a defensive
plea for forgiveness for an action that is open to blame. [From
Wikipedia.]