<computability> (Or "Hamilton's problem") A problem in graph
theory posed by William Hamilton: given a graph, is there
a path through the graph which visits each vertex precisely
once (a "Hamiltonian path")? Is there a Hamiltonian path
which ends up where it started (a "Hamiltonian cycle" or
"Hamiltonian tour")?

Hamilton's problem is NP-complete. It has numerous
applications, sometimes completely unexpected, in computing.