A type is a figure, representation, or symbol of something to come. Such as an event in the Old Testament that foreshadows another in the New Testament. It is someone or something in the Old Testament that 'pictures' someone or something in the New Testament.
There are many types of Christ in the Old Testament that illustrate, proclaim and picture the Lord Jesus.
Noah and the ark, in the book Genesis is a type of the salvation that is in Christ. As Noah was delivered from the wrath of God because of sin in the world, even so we are delivered from the punishment of sin when we are in Christ.