Plus, check out Billboard's Top Hot 100 Songs of the 21st Century chart, Top Artists of the 21st Century chart and Top Billboard 200 Albums of the 21st Century chart, as well as a

The Billboard Hot 100 singles chart measures the top songs every week during the tracking week of Friday through Thursday based on their combination of sales, online streams (audio and video), and radio airplay.

In the 21st century, music became more universal, immediate, and accessible than ever before. On Jan. 1, 2000, the average cost of a CD was about $18, which meant if you wanted to legally own 250 albums,