Espresso is defined by its preparation: an espresso machine moves hot water through a compacted coffee bed under pressure to produce a concentrated drink. The beans themselves can come from different origins, species combinations and roast approaches.
That distinction explains why a bag marked espresso is a recommendation for use rather than a distinct coffee species. Some blends aim for an assertive profile in milk, while others are intended for drinking alone. A lighter-roasted coffee can also be prepared as espresso, although its preferred recipe and taste balance may differ from a darker example.
For a practical description of a shot, state the dry dose and beverage output as well as time and equipment. An approximate volume can change with the crema and is not a complete specification. Taste the result and adjust deliberately. The useful question is whether the preparation produces the balance you want, not whether every shot matches one loosely repeated traditional size.
The conversation
A good question can make a better brew.