About yourself in 160 characters or less
A Twitter Bio shows up in the header of a Profile view, and would be encountered, alongside name and avatar, when browsing a list of Twitterati; both placements make them key for conversion.
In crafting a Twitter Bio users can enter any text, including hypertext. This leaves many choices of content, tone, link strategy and so on: straightforward, ironic, informative, inspirational, cryptic, humourous or even empty, which do you need?