Apologetics is the rational defense of Christianity. It comes from the Greek word apologia (ἀπολογία), which was the term used to make a legal defense in court. The Bible commands believers to engage in apologetics in 1 Peter 3:15 and gives examples of Jesus and the apostles doing it. Modern apologetics covers an array of topics such as the historical reliability of the Bible, morality, science, philosophy, Christian doctrines, and many many more, so there is something for everyone. It incorporates the use of reason, scientific evidence, and history to show that Christianity is true so that people can accept the Gospel message.
Apologetics is valuable for believers and unbelievers. For believers, it is a way to love God with your mind (Mark 12:30), take every thought captive to the obedience to Christ (2 Cor 10:4-5), learn about God and Scripture, give you confidence to share and talk about your faith, and strengthen your faith by removing doubt. For unbelievers, apologetics can help you remove intellectual barriers to faith and have a logically consistent worldview.