Article at the Daily WTF (curious perversions in Information Technology) by Remy Porter on 20 July 2010.
A story relating to a company that sells addresses for use with direct marketing (junk mail). Maintaining lists of addresses is relatively easy, but to have names of residents at those addresses requires more work to acquire and update. Therefore, it is cheaper to use a generic name such as "The resident" or "The car owner." Apparently these generic terms are known as "slug names."
The company in question provided a web based service whereby the direct marketers could go online and download the address lists for a fee. They updated the service so that the customer could choose the cheaper, unnamed list.
The code used by the website checked whether the 'Slug' option was selected, and knew to not include names. However, an oversight meant that an alternative to the name was not supplied, and instead it was labelled "slug." This meant, when mail was sent it was addressed "To the Slug." This was only discovered after several mailings had been sent out.
The underlying cause of this error was in the specification for the code. It simply required the option to be provided to the customer, and did not same anything about how that was to be handled. The code went through full quality assurance, but this simply checked against the original specification.