The term comes from these verses:
Revelation 21:9-10 (Contemporary English Version)
I saw one of the seven angels who had the bowls filled with the seven last terrible troubles. The angel came to me and said, "Come on! I will show you the one who will be the bride and wife of the Lamb." 10 Then with the help of the Spirit, he took me to the top of a very high mountain. There he showed me the holy city of Jerusalem coming down from God in heaven.
The word "lamb" refers to Jesus.These verses and those that follow in this chapter in the book of Revelation refer to and describe the creation of a new heaven, which the Bible labels the new Jerusalem or as these verses call it,the "bride of Christ";which will occur at the end of 1,000 years after Jesus returns (the "Second Coming") to establish a kingdom on earth.