It stands for Not Applicable or Not Available. It means that you don't have the information or that the field in the form doesn't apply to you. Example : in some forms, there is a field where I'm asked to give the years of my military service. As in my country, military service doesn't exist anymore, I didn't do it, but they leave the field for older people who did their time. So I answer "N/A".

hi Hank, NA or N/A may stand for "not available" or "not applicable" :)