Very early in the morning on the day of Jesus' crucifixion, He was questioned by Pontius Pilate, the Roman governor of Judaea. Pilate asked the Lord Jesus Christ, who is the very personification of truth, that infamous question, "What is truth?"
Pilate's question was prompted by Jesus' response to a previous question; Then Pilate said to Him, "So You are a king?" Jesus answered, "You say correctly that I am a king. For this I have been born, and for this I have come into the world, to testify to the truth. Everyone who is of the truth hears My voice." (John 18:37)
Like Pilate, it is very common today for people to try to make truth a personal opinion or at lease a relative concept. You hear statements like, "This is my truth" or "That is your truth". But Jesus said, "...for this reason I have come into the world to testify to THE truth." Truth is not relative and truth it is not a matter of personal definition. Something is either true or it is false.
Satan, the father of lies, and his deluded false teachers, try to distort and diminish the gospel truth of Jesus Christ. Jesus, praying to His Father, said, "Sanctify them in the truth; Your word is truth." (John 17:17) Jesus said to (doubting) Thomas, "I am the way , the truth, and the life; no one comes to the Father but through Me." (John 14:6)
What is truth? The Lord Jesus Christ and the word of God (the Bible) that proclaims His gospel is the truth! Maranatha!