Verisimilitude is a philosophical or theoretical concept that distinguishes truth and falsity of assertions or hypotheses. The problem of verisimilitude is the problem of articulating what it takes for one false theory to be closer to the truth than another false theory.
This problem was central to the philosophy of Karl Popper, largely because Popper was among the first to affirm that truth is the aim of scientific inquiry while acknowledging that most of the greatest scientific theories in the history of science are, strictly speaking, false. If this long string of purportedly false theories is to constitute progress with respect to the goal of truth then it must be at least possible for one false theory to be closer to the truth than others.
Read more about Verisimilitude: Karl Popper