What is what does hiiiii mean?

"Hiiiii" is simply an informal variant of the word "hi". It is a friendly greeting used mostly in text-based communication. The extra "i"s are added for emphasis or to convey enthusiasm. It can also be used as a way to express excitement or happiness when greeting someone. However, it is important to note that using excessive letters or exclamation marks could come across as insincere or immature.