Visible conditions can be used to hide and show fields based on the value of other fields.
A visible condition is written in Javascript and should evaluate to either true or false.
In the visible condition [wt:Field Label] can be used as a placeholder for the value of a field
For example if you want to show an Australian States field based on the value of the Country field, you may have a visible condition like this:
[wt:Country] == 'Australia'