(UK) Synonym of agony column

(graph theory) An unsolved problem in mathematics, asking for the largest possible number of edges in a bipartite graph that has a given number of vertices and has no complete bipartite subgraphs of a given size.

(mathematics) The problem of generalizing Paul Gordan's computational approach to the theorem of the finiteness of generators for binary forms to work with functions having more than two variables.

An insignificant problem of a privileged person.

(creationism, pseudoscience) The conflict between Young Earth creationism (asserting that the universe is thousands of years old) and the starlight-related measurements that show the universe to be billions of years old.

The problem of finding a concept of a taxonomic species that can be usefully applied to many very different types of organism.

(physics, engineering) Any estimation problem designed to teach dimensional analysis or the approximation of extreme scientific calculations: often a back-of-the-envelope problem with limited data.

(mathematics) The problem of finding integer values of n and m for which n!+1=m², where n! is the factorial.

(number theory) The problem of whether each natural number k has an associated positive integer s such that every natural number is the sum of at most s natural numbers raised to the power k.

(philosophy) A problem arising from the tension between the seemingly irreducible nature of consciousness, and its ubiquity. If consciousness is ubiquitous, and every atom (or every bit, depending on the theory) has a minimal level of it, then it is not clear how these tiny consciousnesses combine to create larger experiences.