This is the 667th most frequent Spanish word.
populares
"Populares" means "popular" or "well-liked" in English.
In this sentence, 'populares' is an adjective that describes the noun 'deportes', indicating which sports are popular.
Los deportes más populares son el fútbol y el baloncesto.
The most popular sports are soccer and basketball.
Here, 'populares' again functions as an adjective modifying the masculine, plural noun 'festivales', suggesting which festivals are deemed popular.
Los festivales populares se celebran en verano.
The popular festivals are celebrated in summer.
In this instance, 'populares' is an adjective qualifying the feminine, plural noun 'canciones', denoting songs that are well-known or traditional.