Although “sixth sense” is now commonly used to refer to Extrasensory Perception or ESP, it didn’t originate that way. People have five senses; touch, smell, sight, hearing, and taste. A sixth sense would simply be a sense that goes beyond those five senses, normally one that is unexplainable.
As mentioned, it wasn’t originally thought of in terms of ESP. The term comes from a study that was done in the early 1900’s in regard to visually handicapped people. It was noted and documented that some blind people who were put in a room they’d never been in before could navigate around the room without bumping into objects in the room.
In other words, though they couldn’t see the objects, they could still determine that the objects were there and avoid them. At the time, there were very few theories about how this was possible, so it was unexplained. Thus, the term ‘sixth sense’ was coined to describe some sense that went beyond the normal five senses.
Some more recent studies suggest that this isn’t a sixth sense at all, but rather a heightened sense of hearing. It can be noted, however, that there are people who are both deaf and blind who can still navigate around objects placed in their paths, though they can neither see the objects nor hear sounds reflecting off of them. As of yet, this is still unexplained and it appears that they really might have a sixth sense.