Definition - What does Dirty mean?
In the analysis of a wine, the term dirty refers to any characteristics or physical elements of a wine which are undesirable. A dirty wine is one which shows unhealthy characteristics that can be physically seen; i.e. a wine that is cloudy or lacking bright, reflective quality. It also indicates a wine which has such aromas created by poor hygiene during the winemaking or bottling process.
WineFrog explains Dirty
To refer to a wine as dirty is to say that the wine, from a physical appearance and/or smell and taste standpoint, is undesirable and unfit for consumption. Such wines may appear cloudy due to lack of refinement or protein hazes which have yet to settle. In this case, the wine with some aging may be corrected. These wines will also lack the ability to reflect light and appear dull.
A wine which is described as dirty when referring to the nose (aroma) is indicative of a wine that is sick and not desirable to consume, as it possesses characteristics due to the lack of hygiene during winemaking and/or bottling. These wines cannot be corrected.