The world's definition of joy is: "A feeling or great pleasure & happiness." Notice that this definition depends on feelings, pleasure or happiness; however, joy is far deeper than any of these as joy is independent of them.
The word of God says in Psalm 16:9-10 "No wonder my heart is glad and I rejoice. My body rests in safety...for you will not leave my soul amongst the dead or allow your holy one to rot in the grave."
This joy can only come from Jesus! John 15:11 says "This things I have spoken to you , that my joy may be in you, and that your joy may be full." There is a Greek word for joy and the transliteration is Khar-ah'. This word appears fifty seven times in the New Testament. There are other variations to the word and they appear a total of one hundred and ninety nine times.
The main difference between the secular definition of joy and the reality of believers is this: We should rejoice "regardless" of our circumstances. In fact, we are expected to have joy in the middle of our troubles. Here are five examples of joy...
1) Jesus endured the cross with JOY. Hebrews 12:2
2) Trials and persecutions are occasions for JOY. James 1:2
3) Peter and John found their punishments a reason for JOY Acts 5:41
4) Suffering brings JOY to believers. 1 Peter 4:13-14
5) Paul found JOY in the midst of afflictions. 2 Corinthians 7:4-16
So have JOY since we are redeemed and God rejoices at our redemption.