Anyone who can access a Board can copy a direct link to it. That link can be shared with anyone else, but only people with permission to access the Board will be able to follow the link.
How do I get a direct link to a Board?
Open the Board with which you want to work, then:
- Click
in the top right corner of the Board. - In the resulting drop-down menu, click
.
In the resulting window, either manually copy that link or click 
to quickly copy it to your clipboard.