"Trocas usadas" is a Spanish phrase that translates to English as "used trucks." "Trocas" is the plural noun for truck, while "usadas" is a past participle.
In the Spanish language, nouns and descriptors must agree in both gender and number. Trocas is a feminine, plural noun; therefore, the past participle usado becomes usadas to agree in both gender and number with the noun, trocas.
Though there are many countries that speak Spanish, not every country uses the same vernacular. Troca is a noun most commonly used in Mexico. A more commonly used word for truck in other Spanish-speaking countries is camión.