Depends on what you mean by emoji, but all of the emoji you can use on smartphones and in social media tend to be part of the Unicode standard. They are like any other Unicode character; i.e., they have their own codepoint assigned, and can be represented in a valid Unicode encoding such as UTF-8. Some can be modified with modifying characters (skin colour is a modifiable attribute these days), but this too is not a new feature (e.g., combining diacritic characters do this too, although mostly you would just use the composed variants (like é) instead).