A world for millions
Players create a character, complete quests, collect gear and fight bosses in groups of dozens of people in so-called raids. These required precise coordination over voice chat, a bit like a professional sport.
A cultural phenomenon
WoW had its own vocabulary, memes (Leeroy Jenkins) and even an episode of South Park. For many people it was the first place where they made friends from other countries.
Still going
The game still gets expansions. In 2019 the Classic version came out, bringing back the original world for nostalgic players.