Tags are labels which can be attached to a contact, organisation or opportunity in SET. These can be edited in the “Tag Editor” in your settings page, under “Customisation”.
Once you select the “Tags” option in your settings page, you can then select “Contact Tags”, “Organisation Tags” or “Opportunity Tags”. Click on one of these options to view the full list of tags against that record type.
Click on any of the tags on the resulting screen to view the full list of records which have that tag against them. Here, you can rename the tag, merge it with a second tag and view the full list of contacts/organisations/opportunities which possess that tag. This page also allows you to delete the tag if it is not needed.