Whenever you hear about io games, one of the most common questions is, "What does the io stand for?" or, "What does io mean?" Many players have just accepted the io as a naming trend and very few really know what the term means and how it came to be. Unfortunately there is a lot of misinformation about the origin of io games and the .io domain name.
Many people falsely claim that Matheus Valadares' game agar.io released in April of 2015 was the very first .io game. While agar.io was definitely one of the most popular io games, it wasn't actually the first. Six months before agar.io's launch, Valadares released another multiplayer browser game called cursors.io. Cursors.io was the first known game to use a .io domain name.
By mid 2016, other massively popular io games such as diep.io and slither.io had joined the trend. Pretty soon, io game portal websites started emerging. The first and most popular was iogames.space founded by Mike Tromba in mid 2016. From that point on, the .io domain became directly associated with massively multiplayer online browser games. There is some controversy around whether the term 'io games' accurately describes the genre, however that's a topic for another post.
It's unclear why Valadares initially chose to use a .io domain. His personal email address is me [at] m28.io and according to a Whois lookup, he registered that domain in September of 2014, the month before the release of Cursors.io. Valadares' fondness for the domain was highlighted in a comment he made on the yCombinator Hacker News forums in May of 2015, "I use me [at] m28.io, a lot of people ask 'Is that a real email?' when they see it. It's quite amusing." There may also be a convenience factor with the availability of .io domain names. .io domain names have excellent availability compared with .com domains where almost all dictionary word domains have been taken. Additionally, in computing, io or IO informally stands for input/output which is somewhat relevant to the networking functionality multiplayer browser games rely upon.
Officially, the .io top-level domain is assigned to the British Indian Ocean Territory, the io comes from the 'Indian Ocean' part. While there is no requirement that a person or company has to live or operate in the British Indian Ocean Territory to register a .io domain, io game developers have to pay a premium to use the domain. Generally, .io domain names cost around three times as much as dot coms. For example namecheap.com offers .io domains for $32.99 USD per year and .coms start at $10.99 USD per year.
There is no formal rule that an io game has to use the .io domain. In fact, some io games have simply used the term 'io' in the name and used a dot com domain. For example, the massively popular Paper.io game sneakily disguises itself as an io game, but actually uses a .com domain. Paper.io's real URL is paper-io.com. The developers have since secured the real paper.io domain name as paper.io now redirects back to paper-io.com. Lately, there have been other io games appearing on portals that use many other top level domains such as .space .me and .online.