If the first row of my CSV file contains column headings, what are the valid set of keyword values for the columns?
The column heading have no 'essential' application other than to let you recognise your data. However, CiviCRM makes an attempt to match up the headings in its suggested mapping. To maximize the chance of CiviCRM matching fields correctly, first do an export from CiviCRM of "primary fields." Then copy the appropriate resulting column headings from the CiviCRM export file into your import file.