When your import attempt has failed. You will see that the status of the import is marked as Incomplete. This means the process of data import has been stopped and no data has been imported due to some underlying data or mapping issues. After reviewing the detail, you could resume the data import again by clicking on the resume button. If you click this, you will be able to re-map the imported file and revert any issues that you have found until you could import your data successfully.
Resume Button will only be displayed to all incomplete data import.