A-sides refer to the primary tracks on a music single, typically the most commercially viable or popular song that an artist wants to promote. In the era of vinyl records, the A-side was the side intended for radio play and marketing, often featuring the song that would receive the most attention. In contrast, the B-side is the secondary track, which may be less well-known or serve as a complementary piece. A-sides are crucial for artists and record labels, as they can significantly impact sales and chart performance, influencing the success of albums and careers in the music industry.