Hocus-pocus is a reference to the actions of magicians, often as the stereotypical magic words spoken when bringing about some sort of change. It was once a common term for a magician, juggler, or other similar entertainers. In extended usage, the term is often used (pejoratively) to describe irrational human activities that appear to depend on magic. Examples are given below.
The phrase could have originated from the Roman Canon (Eucharistic Prayer) found in the Latin Mass when the priest performs the transubstantiation of the bread into the body of Christ by saying: "HOC EST ENIM CORPUS MEUM" (meaning - "This is my Body"), which could be misheard as hocus-pocus and associated with magic and changing one object into something else.