(mathematics) The number of ways to partition a set of n objects into k non-empty subsets, denoted by S(n,k).

plural of Stirling number of the second kind

plural of chief petty officer second class

(Canada, Navy) A warrant officer in the Canadian Forces Maritime Command, ranking above petty officer first class and below chief petty officer first class.

(physics, pseudoscience) A perpetual motion machine that spontaneously converts thermal energy into mechanical work.

plural of perpetual motion machine of the second kind