See https://meta.stackoverflow.com/privileges/established-user (privilege earned at 1k rep). Specifically:
How do people see an expanded usercard?
When anyone is viewing your usercard on a question, an answer, or on
the users list, they may hover over your avatar to produce an expanded
usercard that contains extra information. This is also known as a
An expanded usercard is only available if you have have at least 28
characters in their "About Me" section of their profile. You can tell
if your profile is long enough to show an expanded usercard if there
is a drop shadow effect shown on your avatar.
What information is shown on the expanded usercard?
Your expanded usercard will show the following information:
- A larger resolution of your avatar
- Your display name linked to your profile
- Your reputation and badges
- Your Location, if you have entered one on your profile
- A link to your Website, if you have entered one on your profile
- Your About Me section. Up to the first 298 characters will be displayed as the meat of your expanded usercard. HTML links and
linebreaks/paragraphs will be rendered, but not formatting such as
- Any additional HTML links will be displayed and linked at the bottom of the expanded usercard. This does not repeat any links that
are already shown in the previous part.