My own personal response to that famous question of Pontius Pilate about 'What is Truth' is to say that: 'truth' is what happens when our mental image or concept begins to match up with external, factual, reality.

The actual 'reality' out there beyond our mind is ALWAYS more than we can fully comprehend. That is why we always need to 'grow' in 'truth'. As our mental capacity develops, and as more and more people contribute their shared knowledge, our understanding of 'reality' grows. And so our definition of 'the truth' changes as we learn more.