Japanese slang for "uploader", as in somebody who uploads files. Pronounced "upunushi". Combines うp (upload, pronounced "upu") and 主 (master, pronounced "nushi"). Commonly used on sites such as Youtube or ニコニコ (nikoniko, a common video platform in Japan similar to Youtube).

Internet persona(s) who happens to follow you and you happen to follow them back and maintain communication with and have a mutual liking for eachother whether it be friendship wise, etc. (Mutuals if more than one mutual)