My understanding of the terminology is that (1) and (2) are both true, but (1) is stricter.

So, whenever we define a set, we also describe it. But whenever we describe a set, we don't necessarily define it.

So here's an example of a set description that is not a definition: A is a set with three elements.

Here is a definition of a set, which is also a description: Let A = {1,2,3}.