(physics) An electric current in which the direction of flow of the electrons reverses periodically.

(geometry) the internal angles made by two (parallel) lines with a third, on opposite sides of it.

(mathematics) Any function in which the interchange of two independent variables changes the sign of the dependent variable.

(US) Alternative spelling of alternative energy

(physics, cosmology) A hypothetical world situated in a different dimension of space and time than the real world consisting of the universe known and experienced by human beings.

Counterfactual history, a form of scientific speculation used by historians.

(topology) A knot that has a knot diagram in which, in traveling along the knot, one passes through intersections alternatingly: over, under, over, under, etc.

(biology) Each of the two forms of an organism whose life cycle involves alternation of generations, or the fact of such alternation occurring in a given organism.

plural of alternating current

plural of alternate generation