Sets of custom fields
From Planfix
To overcome the technical limitations on the number of custom fields in Planfix, and to make working with them easier, all custom fields are grouped together in Field sets.
By default, there is a Main field set in each account. For the majority of accounts, this set is sufficient; all fields are created in this set. But if you have reached the limit for the number of fields in this set, or if you want to divide up your fields based on business procedures, you can create a new field set.