The Day of Preparation is the name given in Scripture for the day before the Sabbath. Each of the Gospels refers to a day that it calls "the Preparation" (Matthew 27:62; Mark 15:42; Luke 23:54; John 19:14, 31, 42). Mark calls it "the day before the Sabbath." The Jews did not have specific names for the days of the week. Instead, they referred to "the first [second, etc.] day of the week." But the Sabbath was distinctive, and the previous day was used to prepare for this weekly day of rest and worship. Thus, what we call "Friday" the Jews called "Preparation." What was "prepared" is not said. But as no work could be done on the Sabbath, preparations had to be made for food and other necessities.
"The Preparation of the Passover" (John 19:14) is often understood to mean "Passover eve," the day before Passover. This understanding comes from the common use of "the Preparation" for the day before the Sabbath. Outside historical examples of people calling the day before the Passover "the Preparation" do not exist.