Open problem

In science and mathematics, an open problem or an open question is a known problem which can be accurately stated, and which is assumed to have an objective and verifiable solution, but which has not yet been solved (no solution for it is known).

In the history of science, some of these supposed open problems were "solved" by means of showing that they were not, after all, well-defined. Many open problems in mathematics are in fact concerned with the question whether a certain definition is or is not consistent.