This is simply the invoice value of the parts sold. Generally, management accounts separate the different streams of income so that you can see the growth in all areas of the department.
Typically, these different categories are Retail sales, Trade sales with sales to the Service Department and Bodyshop being split between Retail, Internal and Warranty.
Many financial reports show the plit of these different streams of income in the from of a simple pie chart (See Parts Sales Mix)
Example:
Discussion:
In order to calculate many Key Performance Indicators, Parts Sales may need to be annualised (See Annualised Parts Sales). This is simply a projection of your annual sales based on your current performance.