Apparition - Since the early 17th century, this refers to any ghost that seems to have material substance. If it appears in any physical form, including a vapor-like image, it may be called an apparition.

Demons - Historically, this term has included deceased individuals. However, since the early 18th century, it usually refers to an evil spirit, sometimes more powerful than man, but less than Deity. Today, we generally do not use this term to indicate a deceased human being. The female demon, very rarely mentioned, is a demoness.

Ectoplasm - Often referred to as "ecto," this is the physical residue of psychic energy. It's the basis for "slime" used in the Ghostbusters movies. Ectoplasm can be seen by the naked eye, and is best viewed in dark settings since it is translucent and tends to glow. It is very unusual.

EMF - Electro Magnetic Field, or Electro Magnetic Frequency. As the name suggests, it's a combination of electrical and magnetic fields. You'll find high EMF levels around power sources, fuse boxes, electrical outlets, computer monitors, microwave ovens, etc.

Unexplained EMF fields often indicate something paranormal. EMF fields can be measured with various tools, including an EMF meter

Entity - Any being, including people and ghosts.

EVP - Electronic Voice Phenomenon - Disembodied voices of the dead that are not audible at the time of recording. 

EVP Recorder - A tape recorder, or digital recorder, that is used to record the possibility of EVPs. 

Ghost - A sentient entity or spirit that visits or lingers in our world, after he or she lived among us as a human being. We've also seen evidence of ghostly animals and pets.