The Field Name field is the actual field that will be created in the MySQL table to store the answers to this question. As this is a MySQL field, you cannot use spaces or special characters such as backslash (\), asterix (*) etc. You can use any alphanumeric characters and underscores. To avoid problems with exporting to excel, it is best to start and finish your field with an alphabetic character.
The name you chosse for the DB Field Name for each question should obey these rules:
must be unique (for that quiz category)
must not contain spaces, dashes, or other punctuation or special characters
you cannot use reserved words such as "like" or "where". For full list of reserved words, please refer to http://dev.mysql.com/doc/refman/5.1/en/reserved-words.html