When using a Validation service type, the barcode value scanned is validated one-to-one against a database. With secondary validations you can extend validation to include checking the number of scans made during date and time periods.
Valid: The value has been validated against the database and exists in the database.
Invalid: The value does not exist within the validation database.
Invalid Duplicate: The value has been scanned before under the same service. The app user will see when that value has been scanned before.
Advanced: Secondary, Conditional Validations allow you to set counts based on time, date and specified days. Look here for details.