Pilate's response to Christ at His trial, "What is truth?", has been used by many unbelievers as a conversation stopper when talk has turned to eternal things.
Pilate did not have a problem with understanding what truth was. He knew exactly what he expected when he demanded truthfulness from one of his Legion commanders. Pilate's quip really meant "What has truth got to do with this situation, this rabble inciting to riot, and the power I have over you?" Pilate knew what the truth of the matter was but he was not going to decide Christ's fate based on the truth.
Everyone knows what truth is. Just ask them if it would be OK for their banker or accountant to lie to them. They know what truth means when it comes to money. What they may be uncomfortable about is how to determine truth when it comes to religous claims, but the answer is the same as when dealing with money - count the evidence.
Christians should be equipped and prepared to show the truthfulness and reasonableness of our faith.