The book of Jude was named after it’s author. Jude (Judas), a common name of the day, was most likely a brother of Jesus. (Mark 6:3). It’s written to all followers of Jesus, as opposed to a specific church, as it the case with the other letters (also called epistles) in the Bible.
The book of Jude was written to encourage believers in Jesus to “contend for the faith,” (Jude 1:3). It contains criticism about the character and characteristics of ungodly people who have infiltrated the church. As such, it offers effective incentive to persevere in following Jesus, not getting side-tracked or distracted.
The concluding section of Jude is the most well-known portion of this short book; it is often given as a blessing (Jude 1:24-25).