What is truth? One definition I found is 'That which is true or in accordance with fact or reality.'
Ok, so we know what it means. Do you always do that, tell the truth? Are the people you choose to be friends with always truthful with you? How can we possibly know the answer to that? In truth, we can't. We know when we are not being quite truthful, but we can't always tell about other people, even those closest to us.
But there is One, who is closer than a brother, who will never tell you anything BUT the truth. You need not try to figure Him out, you don't have to wonder what He meant by that, and you don't have to decide whether to believe His words or not.
'God is not a man that He should lie; neither the son of man, that he should repent: hath he said, and shall he not do it? or hath he spoken, and shall he not make it good? (Numbers 23:18-20)
Jesus has said He is the truth, the light, and the way. He has proven this over and over again, by word and deed, by His faithfulness, by His very act of being. He is the personification of the word truth.
There are many things God can do, but lie is not one of them. That goes against His nature, Who He is. And guess what? He wants us to be the same.
One of the Ten Commandments is 'Thou shalt not bear false witness against thy neighbor.' (Exodus 20:16) I take that as I should not lie, about people or anything else. If you stand for truth, more often than not you will also receive truth. People know who they can lie to and who they can't lie to. I want to be one to whom they can't. I also want to be one who can help others know the truth.
So keep this word, truth, in your heart. Watch, listen, learn how to be truthful, and how to discern the truth. It's in the Word of the Living God that you will learn of it. When we apply it as a way of life, it will become a way of life.