I think we all know what truth is, or at least we know the concept. Before my daughters were even in kindergarten they would sometimes listen to what I said, and then ask “In real life?” What they wanted to know is whether what I said was something made up, or whether what I said was true.
In philosophy we would say something like “a proposition is true if, and only if, it corresponds with reality.” This classic understanding of truth isn’t dependent on what people think but rather what is. It is this understanding that makes Plato’s allegory of the cave so powerful. We may not agree with everything Plato attempts to establish, but we do all agree we would rather not have all of our beliefs be based off of the shadows on the wall. We want to know reality.
I bring this up because I was amazed when I went to law school that there were professors and highly respected judges who seemed unfamiliar with this understanding of what it means to be true.
Of course, with any word we can change what it means by simply saying over time that this or that concept no longer applies to that collection of letters. “Truth” can start to mean what most people believe etc. But we still would want to know what reality is. That is what makes the truth significant. In other words kids and adults will still wonder whether what they hear is “in real life.”