I guess that someone studying Epicurean Philosophy would fairly quickly grasp the general idea of how the soul is thought of being and dissolving in this materialist context.
So, the Epicureans provide an answer to the questions of the soul, but don't say what it is (at least I think they don't), in a way of a redefinition of a previously superstitious and abstract concept, as they do with the gods (with the explanation of the natural evolution of humans into what they must be), into something related to nature.
For me, it's not that this particular topic is of the utmost relevance, since I think these were just explanations needed to be given by Epicureans to previously existing superstitious concepts in order for the philosophy, and its most relevant contribution of ethics, not to be disqualified as "incomplete". But Still, the problem of superstition is still a real one these days, and being able to provide a bridge to someone to get out of it depends on being able to talk about the things most relevant to them. And I think the soul is one of them, usually.
So, after eliminating what I think would be the previous or traditional conception of soul, a superstitious and abstract "spirit or essence", the only definition I could find (online) is that of the energy (a material thing) that causes the (biological) vigor (an observable and possibly measurable quality of strength of action) that all living things show in different ways.
Is there an "official" one of the philosophy?