True: Property of statements and of ideas: A statement is true iff what the statement means represents a fact. A statement attributing a property or relation to some things is true if the things have the property or stand in the relation. Similarly, an idea is true iff a statement of which the meaning is the idea represents a fact.
This definition is much like Aristotle's definition, except that it is somewhat more explicit about the involvement of meaning. And indeed, one cannot say of a statement that one does not understand the meaning of whether it is true or whether it is not true.
Also, it is intuitively obvious that one understands the meanings of many statements that one does not know are true or false, often for very good reasons: One does not have the necessary evidence or knowledge to confidently assert the one or the other.
See also: Evidence, False, Logic, Methodology, Philosophy of Science, Proposition, Proof, Science, Statement, Truth, Valid
Armour, Stegmüller, Tarski