A 2-D (or 2-dimensional) tax return is simply one that contains a 2-dimensional barcode. This is an extension of the familiar 1-dimensional barcodes very often used on products you buy at the supermarket, clothing store, etc. But, rather than the 1-D barcodes found in such places, 2-D barcodes contain much more information. 2-D barcodes further look like squares or rectangles that contain many small,
individual dots, in contrast to a 1-D barcode, which contains thick and thin vertical lines. A single 2-D barcode can in fact hold a significant amount of
information, including that of an entire tax return.
While the IRS does not yet use 2-D barcodes on its tax forms, many different state departments of revenue do. It's basically a method for them to quickly scan an entire paper tax return and "compterize" it, rather than having a human employee type in every single line, or using an Optical Character Reader software program to do the same work.
Furthermore, several states actually require tax preparation software companies (like TurboTax) to have their state tax forms printable in 2-D format. And in answer to your original question, a non-2-D paper return is simply a valid state tax return form that lacks the 2-D barcode.
For example, and to illustrate the differences, I've created a (hypothetical) Form 140 tax return for Arizona, using TurboTax, with a 2-D barcode. In contrast, I've also also downloaded a blank Form 140 for Arizona from their department of revenue's website. It lacks a 2-D barcode. Both versions of the same Form 140 would be acceptable if they were filed. Please see the images (clickable) at the bottom of this text for visual confirmation.
One final fact to note is that, often, but certainly not always, states will request that paper filed tax returns be mailed to different postal addresses, depending on whether they have a 2-D barcode, or not. This is strictly for their own processing purposes, and doesn't affect your actual income tax refund or liability.
Thank you for asking this question.
