The Song of the Sea (Hebrew: שירת הים) also known as Az Yashir Moshe is a poem which appears in Shemos at 15:1-18. The text describes the destruction of the Egyptian army at the Red Sea, and the future conquest of Canaan by the Israelites. It is included in the Siddur and recited daily at Shacharit.
It is one of only two sections of the Torah that is written with a different layout to the normal simple columns. The alternating words are supposed to represent the two walls of the split sea with Israel walking down the middle. (The other section written differently is Moses' song at the end of the Sefer Torah in Ha'azinu.)
This parshah is also read on the seventh day of Passover, which is the day that the splitting of the Red Sea took place.
After Moses and the Israelites sang the song, "Miriam the prophetess, the sister of Aaron, took the tambourine in her hand; and all the women followed her with tambourines and dances. And Miriam called to them: 'Sing to G-d, for He is most exalted; horse and rider He cast in the sea...'"