Truth is a property of a statement or belief about a fact, or about a relationship between a number of facts, such that it describes this fact, or this relationship, with sufficient precision and completeness for the purpose of a particular inquiry.
The opposite of truth is falsehood.
Falsehood is a property of a statement or belief about a fact, or about a relationship between a number of facts, such that it describes this fact, or this relationship imprecisely or incompletely for the purpose of a particular inquiry.
In both the above definitions we have qualified the precision and completeness of a statement by the purpose of the inquiry for the purpose of which the statement is made or belief held. This is important, because it is beyond human ability to describe anything with absolute precision and completeness. Nor is such description is ever required. All human inquiries have a purpose, which limits the precision and completeness of information sought by a particular inquiry.
Thus a statement: "It is one o'clock", made when the time was 13:05 would be a true statement if the person asking about the time was interested to know approximate time of day. But, if it was important to know the time to the exact minute, then the same statement would have been false.
Statements containing information which is not necessary for the purpose of the particular inquiry are known as irrelevant to that particular inquiry.
Statements can be made verbally or in writing using a language or can be visual representations of reality like pictures, drawings or photographs. Languages are sets of sounds or symbols combinations of which produce mental images in the mind of a person who understands a particular language. To understand a language a person needs to perceive the symbols of the language correctly and to be able to build in his mind the image intended by the maker of the statement. Failure to understand a statement results either in total ignorance of the facts asserted by the statement or in an incorrect (false) image of the facts asserted by the statements being formed in a person's mind. Thus even if a statement is true, it can still be misinterpreted due to misunderstanding.
People make false statements either unintentionally or deliberately. A false statement made unintentionally is due to a sincere but mistaken belief. A false statement made deliberately is called a lie, and is intended to deceive those for whom such statement is intended.
People also have tendency to self-deception. They easily believe what they want to believe, and tend to deny, ignore, or distort the truth of statements which have unpleasant or undesirable to them consequences.
People who make truthful statements and accept the truth of statements made by others regardless of whether such statements are favorable to them or not are known as honest. People who make deliberate false statements or deny, ignore, or distort the truth of statements which have unpleasant or undesirable to them consequences are known as dishonest.
Reality (Nature, Universe) exists independently of the existence of the individuals who seek to describe it or form an opinion about it. Truth does not exist except as a quality of human statements or beliefs. Reality is what exists, it is the human evaluations of it, that are either "true", or "false".