A field name is generated from the value entered in the Label property, unless you supply a different name here when creating ...

A field name is generated from the value entered in the Label property, unless you supply a different name here when creating the field.  Field names cannot be changed once the field is created.

Use only letters and numbers in the field name; other characters may be converted to conform to XML format.  If you enter a name of another existing field, the name will be modified to be unique.