Found in Setup / Core data / Categories from the main menu.
Categories are used in Work Orders, Contracts and Planned Maintenance Events.
The main function behind them is that they provide additional options on reporting for example setting up categories for maintenance, cleaning, asbestos would allow you to view all the requests in these defined categories. If you would like to make it so adding categories to all types of features is compulsory, please contact Dwellant.
Categories are not just used for reporting however, they also have some other useful functions.