If your source file contains columns that do not map to existing fields, create a custom field as part of the import process using the Import Data Wizard.
The Import Data Wizard creates a new field, but does not add the new field to the entity (record type) form or to any entity view. Go to the Customization area to add the custom fields to the respective entity form or view.
The Import Data Wizard uses the same input for the database logical name and the display name. The database logical name must use ASCII A set of non-accented uppercase and lowercase letters A through Z, American English punctuation symbols, and the digits 0 through 9. characters. If this causes a problem, after you import your data, use the Customization area to change the display name of the custom field.
The column header value for a custom field must be 160 or fewer characters. If the column header value has more than 160 characters, the Import Data Wizard cannot create the custom field.