what is .io Domain name?.io is the ccTLD assigned to the Brittish Indian Ocean Territory. It has existed since 1997. Itâs one of the fastest trend currently. Many startup choose .IO for their business especially in Technical niches.io is considered by entrepreneurs to use the extension as abbreviation and it is a better for domain hacks. People see the extensions like .io, .ly & .st from different view and that help the startups gain popularity. io, as in i/o or, in/out.