Baion means a palm branch or frond — the leafy branch of a date palm. Appearing only once in the NT (John 12:13), it describes the branches the crowd took to greet Jesus at the Triumphal Entry. The word is of Egyptian origin (bai = palm tree). In Jewish practice, palm branches were associated with the Feast of Tabernacles (Sukkot) celebration — particularly waving the lulav (palm, myrtle, and willow bundle) in worship.
The crowd's use of baia at Jesus' entry into Jerusalem (John 12:13) is a deliberate Tabernacles-Passover fusion. By waving palm branches and shouting "Hosanna!" (Save now! from Psalm 118:25–26), they enacted the eschatological expectation of the coming Davidic king who would "save" at the feast of final ingathering. Revelation 7:9 shows the redeemed multitude before the throne holding phoinikes (palm branches) — completing the Tabernacles imagery: the ultimate harvest feast of all nations gathered before God. Jesus is the fulfillment of everything the palms pointed to.