1. Go to the contacts section and click on the Name drop down menu next to search you can see a new search option called Name (exclude tags) as shown in red below: 

2. Next search on the tag(s) you wish to omit from the database search – i.e. ‘client’ and then select the search option Name (exclude tags) this will remove the tag group you have selected from your search list.

3. When you have selected your tag(s) you will see contacts will be displayed that do not have the excluded tag applied:

4. The example above shows contacts who do not contain the tag 'email-campaign', 'north-west' and 'summer-promotion' as this tag group was excluded on the search.

Please note you can omit more than one tag group from the search. Just go back to the tag search and click on another tag and then it will remove that tag too.