(mathematics) A mathematical problem in which lines drawn from two points in the plane of a circle must meet at a point on the circumference, making equal angles with the normal at that point.

(euphemistic) A child who is particularly difficult to raise or educate, especially due to a lack of self-control and disruptive and antisocial behavior.

An observation that contradicts an accepted law or theory.

A mental representation of a particular problem, including initial, final and possible intermediate states

(mathematics) The problem of finding the "best" solution from all feasible solutions, given constraints defining which of the solutions are feasible, and a goal function defining which of the feasible solutions is the best one.

The problem of whether prescriptive statements—stating what the case ought to be—can be derived from descriptive statements—stating what the case is.

(philosophy) the philosophical problem involving our ethical obligations to future persons which derives from the observation that different courses of action will result in entirely different, or nonidentical, persons coming to be.

A communication problem where a person seeking help (for example, from a computing helpdesk) provides misleadingly incomplete information about the source of the problem and thus receives inaccurate or unhelpful suggestions about how to fix it.

The problem that the meanings of symbols cannot be grounded, but require more symbols to explain them.

(philosophy) The epistemological problem that a description of knowledge as "justified true belief" is not adequate: there are counterexamples where an individual has justified true belief of something and yet does not know it to be true.