Fields are the individual elements that hold data in your application. This could be a price, for example, an instrument name, an instrument code, or a date. Every basic individual item of data you need has to be defined as a field.
A single field can be used in multiple tables.
You define your fields in a specific file that has the name application-fields-dictionary.kts.
So, if your application is called heracleum, the file name will be heracleum-fields-dictionary.kts.