The term umbral calculus has two related but distinct meanings.
In mathematics before the 1970s, "umbral calculus" referred to the surprising similarity between seemingly unrelated polynomial equations and certain "shadowy" techniques used to "prove" them. These techniques were introduced by John Blissard and are sometimes called Blissard's symbolic method.[1] They are often attributed to Édouard Lucas (or James Joseph Sylvester), who used the technique extensively.[2] This use "shadowy" techniques was put on a solid mathematical footing starting in the 1970s, and the resulting mathematical theory is also referred to as "umbral calculus".