definition

A technique for contributing to a Roth IRA when income exceeds the contribution limit.  Non-deductible contributions are made to a traditional IRA, and subsequently the traditional IRA is converted to a Roth IRA.

commentary 

For those high income earners who have maximized their retirement plan contributions,  backdoor Roth contributions can be a good choice.  Since the contributions to the traditional IRA have already been taxed,  the conversion is tax free.  Note, however, that due to the IRA aggregation rule , the existence of a prior before-tax traditional IRA will cause a portion of the conversion to be currently taxed.