Good Friday is the day Christians commemorate Jesus Christ dying on the cross for our sins. The Bible says that on Friday Jesus laid down His life for us and died on the cross for our sins. Three days later, on Easter Sunday, He rose from the dead!
The question is, why do Christians call it Good Friday if it was the day that Jesus went through unimaginable suffering and then died? While the exact reason is not clear, the best explanation seems to be that the word "good" originally referred to goodness, or holiness. So to call a day "good" meant to call it "holy." If we look at it that way, then "Good Friday" could really be called "Holy Friday" and it makes sense.
It is also interesting that, in other languages, Good Friday is called by other names. The same day in German could be translated "Suffering Friday".
What is important is that, on that day and always, we recognize the wonderful gift of God in giving His Son Jesus Who went through horrible sufferings and then death for us, so that we might be freed from the burden of sin. Thank you Jesus!