Paraskevidekatriaphobia (you try to pronounce it) is the term, like other phobias, to describe a morbid and irrational fear of something, in this case Friday the 13th.
The word that is derived from the concatenation of the Greek words Παρασκευή, δεκατρείς, and φοβία, meaning Friday, thirteen, and phobia respectively; alternate spellings include paraskevodekatriaphobia or paraskevidekatriaphobia.
TRIVIA: In any given year there will be at least one and at most three Friday 13ths.
If you were a teenager in the 1980s and 1990s the first reference that comes to mind with this supposedly ominous date is the series of horror films, yet the superstition surrounding this date-meets-day recurrence is actually much older.
The concept of Friday the 13th being a day of bad luck occurs in English, German, Polish and Spanish cultures (in Greece and Spain it's Tuesday 13th).
Despite many people exploring historical references and even taking studies to see if in fact Friday the 13th is unluckier than other days no absolute explanation for the superstition can be identified.
A number of researchers can attribute reasons for the naming of either Fridays or the number 13 as being unlucky but few can categorically connect the two prior to the early 1900s.
Some theories include historical references to the arrest of many of the Knights Templar on Friday, October 13, 1307 by King Philip IV, or because Judas was the 13th Apostle who betrayed Jesus who died on a Friday.
Other theories relate to the ancient Egyptians, the sacking of Constantinople, Eve giving apples to Adam and so on.
Personally, the day doesn't affect me but I have to say with all the 'historical' material to draw from you'd think the film producers could have come up with a better story scenario than a hockey mask wearing psycho bumping off kids at summer camp. Seriously, the lack of imagination and the lost story line opportunity is far more disturbing than the blood thirsty films (all 14 of them).