As I detailed in “Emojibake” are considered harmful, Twitter has allowed users to use the Unicode Private Use Area character U+EA00 to represent its logo.
This has caused confusion on non-Twitter run websites which aren't using Twitter's proprietary “Chirp” (GT America with tweaks) font.
This is a free (CC0) icon font which has only two glyphs: .notdef and uea00, which is the Twitter logo. If you are browsing the web and are tired of seeing on random pages rendered incorrectly, then this font will fix that.
Note that Twitter's logo is a trademark, and although there are no copyright claims on this font, your use of it must comply with trademark law in order to be valid in your jurisdiction.
This font's author, Fredrick Brennan (@ctrlcctrlv), is not and has not ever been an employee of Twitter, Inc. This font is not affiliated with Twitter, Inc. in any way. It is just an icon font with one icon.