Apologetics is the field of theological study that deals with the reasoned and systematic defense of the truth of Christianity. The term “apologetics” comes from the greek word apologia (απολογία), which is translated “to give a reply” or “to make a defense.”
but in your hearts honor Christ the Lord as holy, always being prepared to make a defense to anyone who asks you for a reason for the hope that is in you; yet do it with gentleness and respect,
—1 Peter 3:15, ESV
κυριον δε τον θεον αγιασατε εν ταις καρδιαις υμων ετοιμοι δε αει προς απολογιαν παντι τω αιτουντι υμας λογον περι της εν υμιν ελπιδος μετα πραυτητος και φοβου
—1 Peter 3:15, 1894 Scrivener Greek New Testament
As believers and followers of Christ, we are always to be prepared to give a defense for the reason for the hope that is in us.
Related: Wikipedia entries on Apologetics, Christian Apologetics and Presuppositional Apologetics