The first character in the Unicode Private Use area, or "U+E000". It is often used to display specific non-cross-platform characters in specific operating systems or in specific applications. Sometimes it is used to display the Tux logo in
Linux (Libertine Font). On twitter, it is used for the left down
arrow. It is not a null character ( ) and it is not an Emoji that isn't being displayed correctly (). The
box with some letters and numbers in it (hexadecimal
code point) is sometimes referred to as "tofu".