Gallera literally translates to "cockfighting arena." It's a very specific and culturally significant word in many Spanish-speaking countries, particularly in the Caribbean.
In this song, Juan Luis Guerra uses gallera as the central theme, where the narrator loses everything he owns due to gambling on cockfights. The repetition of the word emphasizes the devastating impact of this activity on his life, making it a memorable and unique word to learn.
“La Gallera” (“The Cockfight Arena”) turns a night at the ring into an inventory of everything a man throws away chasing one more bet. He starts small — “Mi gallo, Candela” [“My rooster, Candela”], his best spur, a jacket he brought back from abroad — then the losses widen to “Mi tierra, mi finca, mi casa, mi perro” [“My land, my farm, my house, my dog”]. By the later verses the list turns almost comic: his voter registration card, his shaving table, his pillow, even “mi alma” [“my soul”], all stacked onto the same chorus he keeps repeating, “Perdí en la gallera” [“I lost at the cockfight arena”]. Juan Luis Guerra sets the whole confession to a driving merengue groove, so the singer's ruin keeps dancing even as the tally gets worse.