There are two primary varieties of beans, arabica beans and robusta. An expresso bean (arabica) is generally darker (roasted longer) with more visible oil.
People didn’t like my answer, so maybe this site would better explain:
Nevertheless, when you compare espresso beans vs. regular coffee beans, you’ll notice the former is always dark roasted and oily. This is not to say that regular coffee beans cannot be dark and oily. However, they can feature other characteristics as well, while for espresso beans, these qualities are non-negotiable.
There are two primary varieties of beans, arabica beans and robusta. An expresso bean (arabica) is generally darker (roasted longer) with more visible oil.
People make drip coffee with Arabica beans
People didn’t like my answer, so maybe this site would better explain: