You can add labels with custom names to a card. This will help you to tag cards for example by their purpose.
To assign labels to a card, click on the Labels button and select Add Label.
Choose desired Labels for a card. Your choices will be automatically saved.
Tip: New labels can be also created from inside of Card. Simply go to Labels section and then click Add labels. Here choose to create a new label (set a name and color for it).
You can also assign Labels using Quick Actions in the Board's view.
Labels added by you will be visible in Card's view as well as in Board's view.
Labels on a Card in Board's view - you can use a filter to see only cards with chosen labels.