Paraskevidekatriaphobia is a medical term, derived from the Greek language, used to nominate the fear of Friday the 13th. (paraskevi—Friday; dekatreís—13; phobia—fear). The day (one of which occurred this past week) is considered by many a day of bad luck, though such a correlation with the date seems to be of relatively recent origin, (the last 150 years or so).
The term phobia is used to designate an extreme or irrational fear or aversion. Consider the following quote from Wikipedia:

