E.g. in a domain model with two aggregate roots:
Is there a specific term that refers to a collection of aggregates of the same root type (e.g. a collection of books)?
In Confusion about the meaning of the word aggregate in domain driven design I read the term aggregate type, which might or might not fit, but I haven't found a direct mention in Evan's blue book.
Is there a specific term that refers to a collection of aggregates (e.g. books or authors)?
No.
Keep in mind that the definition of aggregate is
A cluster of associated objects that are treated as a unit for the purpose of data changes. External references are restricted to one member of the aggregate, designated as the root. A set of consistency rules applies within the aggregate's boundaries.
A union of two different transactional units is... not very interesting.
