Psychohistory is a fictional term first described in Isaak Asimov's classic novel Foundation
Psychohistory is a branch of mathematics which deals with the reactions of human conglomerates to fixed social and economic stimuli.
In a nutshell
it's the science that can predict the future.
The greatest psychohistorian of all time was Hari Seldon
"I quite understand that psychohistory is a statistical science and cannot predict the future of a single man with any accuracy."