Fiesta comes from Spanish fiesta (festival), from Latin festus (joyful) — the same root that gave English feast, festival, and fête through different Romance languages.
A festival, celebration, or lively party, especially one with a Spanish or Latin American character.
From Spanish fiesta, meaning 'feast, festival, holiday,' from Vulgar Latin festa (festival), from the neuter plural of Latin festus (festive, joyful). The Latin root also gave English feast, festival, festive, and fête. English borrowed the Spanish form to evoke a specifically Spanish or Latin American style of celebration