Anonymity on the Internet applies to any interaction a user has on the Internet that protects his or her identity from being shared with another user or with a third. anonymity. Play an·o·nym·i·ty. Use anonymity in a sentence. LINK / CITE ADD TO WORD LIST. noun. The definition of anonymity is the quality of being unknown. anonymity definition, meaning, what is anonymity: the situation in which someone's name is not given or known. Learn more.