is the (smallest) unit of an article range that can be distinguished by number and designation. A. are often also referred to as goods or merchandise. The term “number of articles” should always refer to the size or quantity of an assortment (articles on the books or in stock).
The terms “quantity of items” or “number of items” are imprecise, as there is a risk that they refer to the number of item units. To make a clear distinction (if there is a risk of confusion), the term

the term “number of articles” should be used when the generic term “assortment” is meant,
the term “number of item units” should be used when the generic term “stock” is meant.

Source: logipedia / Fraunhofer IML