Truth is a description for something which conforms with fact or reality.
Types of truth
From a scientific perspective there are two kinds of truth: contingent and logical.
A contingent truth is one whose validity is contingent on other facts which may or may not be true or known. An example is whether there exists intelligent life in a distant galaxy. Since we know, as a proof of principle, that intelligent life exists in our galaxy, and we don't yet understand the conditions that gave rise to it, we may accept the possibility that it could exist in another galaxy. Since we have very little information about conditions in distant galaxies, and we will probably never have sufficient information to answer such a question, the only reasonable answer to that question is that we don't know, and probably never will. A reasonable, fair, and open-minded person must be agnostic on that question.
A logical truth is one whose validity depends only on logic, on the definitions and properties of concepts we ourselves define. An example is whether 2 + 2 can equal 5. It follows from the definitions of the symbols 2, 4, 5, and +, and of "equals", that 2 + 2 can only equal 4, not 5. It is not necessary for a reasonable, fair, and open-minded person to remain agnostic on that question. There is nothing contingent or unknown about it. (Still, even logical truths rest ultimately on definitions and axioms. Thus, whether logical truths comport with what we see in reality is an entirely different matter. See also the Wikipedia articles on the philosophy of logic and philosophy of mathematics.)