The bride of the Lamb is the Church, the People of God.
The Church/People of God as Christ’s bride is a theme throughout Scripture:
For I am jealous of you with the jealousy of God, since I betrothed you to one husband to present you as a chaste virgin to Christ.
And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband.
On that day—oracle of the LORD— You shall call me “My husband,”
For your husband is your Maker; the LORD of hosts is his name…
I passed by you again and saw that you were now old enough for love. So I spread the corner of my cloak over you to cover your nakedness; I swore an oath to you and entered into covenant with you—oracle of the Lord GOD—and you became mine.
In the Gospels Christ also often refers to Himself as the Bridegroom.