Good Friday is the solemn celebration of the Lord's suffering and death on the cross. Some congregations will remember the 3 hours of darkness from noon till 3pm with a tenebrae (darkness) service. Good Friday is in Holy Week.
Calling the day of the Crucifixion ‘Good’ Friday is a designation that is peculiar to the English language. In German it is called Karfreitag. The Kar part is the ancestor of the English word care and it meant mourning. So in German it is Mourning Friday, which is what the disciples did on that day. They mourned because they thought all was lost
Good Friday may have meant God’s Friday, like good-bye meant God be with ye. We call it Good Friday because Jesus' death on that day bought us the greatest good of all, eternal life with God