In order to distinguish one contact from another by any special properties, you can add tags. For example, to capture the peculiarity of the customer when choosing a product so that the manager contacting the customer always paid attention to this feature.
To start working with tags, you need to go to the contact card, lead or company and click the "Add tags" button, located on top, next to the name. Then, in a dropdown box, you can select a tag from the already existing ones, or create a new tag by starting to enter its name. When you type a tag from the keyboard, the match with the already created tags is taken into account. You can always select a tag from the list, or create a new one by entering its name.
You can also add a new tag by going to "Search and Filter", then "Manage" and enter a new tag there.