The “selection filters” option is used to filter the list of records contained in the linked app, this is ideal for large data sets. When you create the selection filters, you can select a field in the app that contains the record links choices (right column) that will be used to filter records based on a field in the linked app (left column).
Similar to the visibility and required rules, you can set the operator for a rule to one of the following options: equal to, not equal to, contains, starts with, greater than, less than, is empty, is not empty. This allows for creating very narrowly focused rules to help provide the user with only options that meet the criteria.
In the example image above we have a sales app that is used to capture sales information. Inside this app, we link to another app that has all of the customer data. The selection filter is setup so that the store number field in the customer app will be used to filter the results provided to the user by matching the value to the value in the store number field in the sales app.