The Hebrew noun yam (יָם) means sea, particularly the Mediterranean Sea ("the Great Sea"), but also refers to large bodies of water generally, including the Red Sea and even the Nile. It appears over 390 times in the Old Testament and carries both geographical and cosmological significance.
Because the Mediterranean lay to the west of the land of Israel, yam also came to mean "west" — the sea-direction. This is why the tribal allotments often describe borders running "to the sea" meaning westward. The word encompasses the literal sea, the direction west, and the symbolic realm of chaos and depth.
In the ancient Near East, the sea was often associated with chaos, danger, and primordial forces opposed to order. Canaanite mythology personified the sea as Yam, a deity of chaos who battled Baal. Israel's scriptures counter this worldview: YHWH created the sea, commands it, and uses it for His purposes. He parted the Red Sea for Israel's deliverance and stilled the storm for His disciples.
The prophets use the sea as a symbol of Gentile nations (Isaiah 60:5) and of unstable, tumultuous powers (Daniel 7:2-3; Revelation 13:1). But the New Jerusalem has no sea (Revelation 21:1) — the symbol of chaos and separation from God is abolished when all things are made new. In Christ, the waters that once threatened become the waters of baptism — death that issues in life.