Psi is a blanket term referring to all parapsychological phenomenon. It is divided into two types:
- Psi-Gamma: This refers to cognition, e.g., extrasensory perception and remote viewing.
- Psi-Kappa: This refers to action, e.g., telekinesis and street light interference.
Parapsychology is considered to be on the fringe of standard science, due to its difficulty in testing and measurement. Demonstrations of parapsychological phenomenon can, however, be observed.
The field was created by Joseph Banks "J.B." Rhine, a graduate of both Wooster College and Ohio Northern University in Ohio. He attended graduate school at the University of Chicago in the early 1920s, earning a Master's and Ph.D. in botany. He then attended Harvard University to study psychology with psychologist William McDougall. McDougall left for Duke University in 1927, and Rhine went with him. While at Duke, Rhine attended a lecture by Sir Arthur Conan Doyle, and was amazed. He began experimenting with extrasensory perception through psychological tests, and would later test psychokinesis. He continued his studies at Duke for many years, founding the Foundation for Research on the Nature of Man in the early 1960s. It was Rhine and McDougall coined the term parapsychology. Today, the FRNM is the Rhine Research Center Institute for Parapsychology, and continues research in parapsychology.
Other terms 
Anomalous operation is a term used to describe the use of psi to explain paranormal activity.
Paraphysics is a term of debated definition. It dates back to the late 19th century; however, many varied definitions have been used, and as a term, it is not widely used. A more modern definition differentiates paraphysics and parapsychology by saying the focus is on physics and psychology respectively. However, such a small part of parapsychology extends into physics that it is not studied as a science.