A hosanna is a statement or exclamation of praise. Usually, hosannas praise God.
The noun hosanna referring to a cry of praise can claim a long pedigree in English: it first appeared in the 12th century. It's from a Biblical Hebrew phrase meaning "Pray, save us." Hosanna made stops in Greek and Latin before arriving in English in the earliest translations of the Bible. Any kind of thanks and adoration aimed at God could be considered a hosanna. In church, many of the prayers and songs are hosannas.