Your guild and its description is visible to all users. If only guild members should be able to read the description or parts of it, you can exclude non-members by following this tutorial.

Example of a guild description:
Code:
 
Guild meeting on xx.xx.xxxx at xx:xx
 
Welcome to guild X
Want to become a member? [URL]http://xxxxxx.xx/xxxxx[/URL]
As non-members of your guild should be able to read only the Welcome-section but not the date of your meeting, you can add ///.

Code:
 
Guild meeting on xx.xx.xxxx at xx:xx
/// 
Welcome to guild X
Want to become a member? [URL]http://xxxxxx.xx/xxxxx[/URL]
Now non-members can only read:
Code:
 
Welcome to guild X
Want to become a member? [URL]http://xxxxxx.xx/xxxxx[/URL]
Note: you can split the guild description by adding ///. Upper part: readable by members only, bottom part: readable by everyone.
However, it is not possible to have more than two parts.