(Hebrew) = meaning to save, rescue, savior. In liturgical context, it refers to a cry expressing an appeal for divine help. Also, it was the shout of praise or adoration made in recognition of the Messiahship of Jesus on His TRIUMPHAL ENTRY INTO JERUSALEM.

Palm Sunday is celebrated as the TRIUMPHAL ENTRY into Jerusalem. It is the last seven days of Jesus’ earthly ministry here on earth. He was being honored as The King.

In Luke 19:30 Jesus instructs two of his disciples to go into the village Bethphage and where to find the colt. They bring it to Him - a donkey that has never been ridden before. The disciples laid their coats on the donkey, then Jesus sat upon it.

And most of the crowed kept spreading their garments on the road, and others kept cutting branches from the trees and scattering them on the road. (Matthew 21:8)

And the crowds that went ahead of Him and those that followed Him kept shouting, HOSANNA (O be propitious, graciously inclined) to the Son of David, the Messiah! Blessed (praised, glorified) be He Who comes in the name of the LORD! HOSANNA (O be favorably disposed) in the highest (heaven). (Matthew 21:9)
[see also Psalm 118:26]