That moves backwards and forwards.

(religion, historical) A member of the Family of Love religious group in 16th-century England.

(mathematics) Any function whose value repeats after the regular addition of a period to its independent variable; i.e., a function ƒ such that, for some positive constant p, ƒ(x + p) = ƒ(x) for al...

Not emitting peeps or a peep.