For example World of Warcraft from Wiki (mainstream game)
World of Warcraft was the best-selling PC game of 2005 and 2006.[91] As of January 22, 2008, World of Warcraft had more than 10 million subscribers worldwide, with more than 2 million subscribers in Europe, more than 2.5 million in North America, and about 5.5 million in Asia.[92] At its peak in October 2010 the game had 12 million subscribers.[93] As of February 2014 the game has 7.8 million active subscribers.[94] On January 28, 2014 Blizzard announced that 100 million accounts have been created for the game.[95]
The important number being 100 million users of WoW in it's history since that is the total amount that has at least played and paid for the game.
Now 100M is probably the number of accounts created including trials. Which likely includes me, and I downloaded the client logged in for 5 minutes and left didn't pay anything at all... +1 account... And I'm not ever going back.