Something that is expressed in a different way, not known or explained but made a more simpler matter.
Well you know the story with cain and abel. God accepted abel's offering of animal (blood) and rejected cain's offering of food ( That is works cause it takes work to til ground plant seeds and to harvest it) That is symbolism for God in the new testament rejects works as a means of salvation but only the blood of Jesus Christ can save. Or another one is God asked Abraham to sacrifice His son, but saved Abraham's son. That was symbolism for God to sacrifice His son in the new testament. It Goes on and on. When Moses lifted up the serpent in the wilderness it was a bronze snake on a pole. The bronze represents mankind, the serpent represents sin. They lifted Jesus up on the cross so He could become sin. 40 represents the number for testing. God let the jews wonder in the wilderness 40 years. Jesus was tempted 40 days. God is very smart and He uses symbolism in the old testament to for tell the new testament.
The Canadian flag contains a maple leaf, which has long been a symbol of Canadian things.