What are exactly considered resources in modern economics? I'm taking a basic course in economics and I'm trying to understand what the term "resources" really mean in this context.
Reading this article, I found out that in classical economics, resources are usually divided in 3 categories: Land, Labour and Capital.
Anyway, while watching some videos, often I see enterpreneurs as another possibile type of resource.
Now, is this an addition of modern/present economics?  

**I've seen that often "modern" and "classical" economics are interchangable attributes referring to the same thing: the view of economics started with the works of Adam Smith
What I think you want to consider to be grouped with land, labour and capital is another factor to be considered with labor- technology (A.K.A "Knowledge*).

The term "technology" here means an augmenting factor which is external to the present amount of labour. This can mean improved machinery to produce goods and services or alternatively, this can be viewed as a improvement in human capital which is what training employees can be viewed as in terms of technology.

For more information about the effect of technology/improved human capital in economics, I would recommend checking out the Solow Model and the Skill premium Model

Hope this is helpful!