The Unicode Standard is maintained by the Unicode Consortium, it is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems.

So the unicode version refers to the character encoding version released by the Unicode Consortium. Unicode releases new versions almost every year, and each new version contains more new character encodings, within also contains new emojis. The updates of these versions ensure that more characters are displayed in a unified and compatible way, so that people all over the world can reduce communication barriers on internet.

Recently released Unicode 14.0, it adds 838 characters, including 37 new emoji, a total of 144,697 characters.