What does "Certified" mean, and what is the difference between Units shipped and Album's sold. This question keeps coming up in the comments here, so here is a little information to help explain it.
According to the RIAA Site Recording Industry Association of America, an artist's record label will inform them of their intent to "Certify" a recording artist. The label pays for said certification, and bases this on following according to the RIAA
It’s probably worth taking a moment now to explain what we mean by ‘shipments’. We collect data directly from the record companies, rather than from the stores that sell recorded music to the final consumer. Hence, the term “shipments” as in “shipments from the record labels to the stores they supply.” Since stores can return unsold merchandise, we subtract returns so the final data you see is a net figure (keep in mind sales and shipments are virtually the same thing for digital products). Overall, “shipments” and “sales” are very similar, but we use the term shipments for accuracy. A frequent question we get is whether our data represents the whole US market, or just the RIAA member companies? Our aim is to describe the whole market, and we use independent estimates to account for the parts that are not created or distributed by the major record labels.
Historically, these reports have focused on sales of physical goods like records, tapes, and CDs. As we moved into the digital era, the reports expanded to include digital downloads, mobile sales, and subscription services. Now we’re seeing an explosion in new platforms for music listening like Internet and satellite radio, and social networks, where fans can listen to streams of music instead of buying them directly. Traditional metrics of album sales and downloads no longer tell the whole story.
Additonal Certification Information:
Several different thresholds have been in use at different times and places for both album and single awards. Some of these were based on units sold and others on the value of retail sales. The first official designation of a "Gold record" by the RIAA was established for singles in 1958, and the RIAA also trademarked the term "Gold record" in the United States. On March 14, 1958 the RIAA certified its first Gold Record, Perry Como's hit single "Catch a Falling Star". The Oklahoma! soundtrack was certified as the first Gold album four months later. In 1976, RIAA introduced the Platinum certification, first awarded to Johnnie Taylor's single, "Disco Lady", and to the Eagles album, Their Greatest Hits (1971–1975).
Like many record industry awards and rankings, the measurement is based on wholesale shipments to all types of retail outlets, and is not based on actual retail sales or financial transactions. As a result, an early award or ranking for a new release reflects only the distributor's market power expectations.
Certifications no longer apply solely to physical media.