The domain extension .io is a ccTLD, i.e., a country-specific, top-level domain, which was assigned to the British Indian Ocean Territory and introduced in 1997. The domain is administered by the domain registrar Internet Computer Bureau (ICB), which is based in the United Kingdom and since 2017 has been a subsidiary of the American group Afilias, which also administers the TLDs .info, .mobi, and .pro, among others.
From the very beginning, the .io domain was not meant to be a country-specific extension – which is not surprising given the fact that there are no legal permanent residents of the British Indian Ocean Territory. As such, any individual or legal entity can register a .io address regardless of residency or establishment, and 2 to 63 alphanumeric characters may be used. Only addresses with second-level domains like .com, .net, or .gov are blocked. In other words, registering a domain like mybusiness.net.io is not possible.