Here is a list of definitions of the word "apologetics" from both presuppositional and classical/evidential apologists:
“Christian apologetics is, at root, a biblical discipline.” Richard Gaffin Jr. in K. Scott Oliphint and Lane G. Tipton, eds. Revelation and Reason: New Essays in Reformed Apologetics (Phillipsburg, N.J.: P&R Publishing, 2007), 1.
“Apologetics is about inviting people to look into the face of this absolute, personal God. It dares them to see him for who he is and what he means for the world.” Thom E. Notaro in Revelation and Reason, 157.
“We may define it as the discipline that teaches Christians how to give a reason for their hope.” John Frame. Apologetics to the Glory of God (Phillipsburg, New Jersey: P&R Publishing, 1994), 1.
“Apologetics is the vindication of the presence of Christ as his church against the various forms of the non-Christian philosophy of life that constantly attempt to invade and intrude that presence.” William D. Dennison in Revelation and Reason, 203.
“Apologetics is a way of doing theology, a way of doing evangelism, a way of doing philosophy.” Greg Bahnsen in Van Til’s Apologetic (Phillipsburg, NJ: P&R Publishing, 1998), 44-45.
“Apologetics may be defined as persuading people to think through their worldviews, abandon their false beliefs, and embrace Jesus, all while defending the truths of the gospel.” Jamin Hubner, Light Up the Darkness (BookSurge, 2008), 119.
“Apologetics is the reasoned defense of the Christian religion.” R.C. Sproul, John Gerstner, and Arthur Lindsley. Classical Apologetics (Zondervan, 1984), 13.
“Apologetics…is that branch of Christian theology which seeks to provide a rational justification for the truth claims of the Christian faith.” William Lane Craig. Reasonable Faith: Christian Truth and Apologetics (Crossway, 2008), 15.
"Apologetics is the discipline of defending Christianity as true, rational, and pertinent to life." William Lane Craig. On Guard: Defending Your Faith with Reason and Precision (Colorado Springs:David C. Cook, 2010)
“Apologetics is directed primarily for those who do not believe so that they may have a reason to believe.” Norman Geisler. “An Apologetic for Apologetics.” http://www.normangeisler.net/apologetic.html
“At its essence, apologetics is the art and science of Christian persuasion: communicating the relevance, coherence, and reasonableness of the Christian Gospel to skeptics, cultural influencers, and critical thinkers across the globe.” Ravi Zacharias International Ministries. http://www.rzim.org/initiatives.aspx
“Apologetics is the attempt to ally reason to faith, to defend faith with reason’s weapon.” Peter Kreeft and Ronald Tacelli.Handbook of Catholic Apologetics: Reasoned Answers to Questions of Faith (Ignatius Press, 2009), 32.