Good Friday is the Friday before Easter, the day on which Christians annually observe the commemoration of the Crucifixion of Jesus Christ. It doesn't seem to be a day that would be considered "good." That is because it probably was never intended to be "good" or even a Friday.
Good Friday is called "good" only in English. We don't really know the origin of the day's name but some say it is from "Gottes Freitag" meaning "God's Friday" or from the the German Gute Freitag. However, the Gute Freitag explanation seems weak because Germans call this day Karfreitag meaning Sorrowful or Suffering Friday.
The Anglo-Saxons called it Long Friday. In other countries, it is known not as "good" but as Holy Friday, Black Friday, Great Friday, Long Friday, and Silent Friday.
The phrase "Good Friday" does not appear in the Bible. The word Friday isn't in the Bible. Actually, the days are called by numbers. The seventh day is the Sabbath and the other days are first, second, third and so on.
According to the Jewish calendar, Jesus died on 15 Nisan, the first day of Passover and translated to the Gregorian (Western) calendar, that would be April 7. But Christians determined not to commemorate it on a fixed date and followed the varying date of the Jewish Passover which conforms to the Jewish lunisolar calendar (rather than the Gregorian solar calendar).
That connected Jesus' Last Supper with his disciples on the evening before his Crucifixion to the Passover seder. Despite this "inaccuracy," this dating has continued making Good Friday (and so, Easter) fall between March 20 (the first possible date for Passover) and April 23.
Catholic and Protestant churches say that Jesus was killed on Friday and resurrected Sunday morning, the year given as 33 A.D. The Early New Testament church did not observe an Easter holiday, but to move people away from celebrating the Biblical Christian Passover, the Catholic Church appropriated a pagan holiday of the goddess Ishtar (Astarte) who was worshiped by Babylonians and Assyrians who was celebrated around the spring equinox.
Other Biblical scholars interpret Jesus' crucifixion at being 3 p.m. on a third day (Wednesday not Friday) in 30 A.D. After 3 days and nights in a tomb, he was resurrected on our modern day Easter.