You might have data with similar field values that can be grouped or categorized in a particular way. You can assign tags for such values while Setting up data collection.. For more information, see
Tags must be added only if they might be useful in search filtering. Tags have some performance overhead associated with them, so you must think through a clear tag convention ahead of time and only define those tags that will be used. To be able to assign tags (while creating a data collector), you must first define them by navigating to Administration > System Settings. For example, if you have a field for the host name of computers that are used at various locations, you might want to assign a tag for the location from which the data is generated. You might also have tags for the department or the operating system from which the data is generated.
Under the Filters panel on the Search page, for every tag, a count of occurrences is displayed in parenthesis () next to the tag name. If the number of occurrences is too large, an approximate count is displayed with a plus sign (+). When you expand such a tag, the values show the approximate count with an asterisk (*) next to them. The plus sign next to the tag name and the asterisk next to the tag values indicate that the count for those tags or values is an approximate number, not an exact number. If you select one of the tag values to add it to the search criteria and click Search, the accurate count is displayed next to that value.