Transactionally Consistency in DDD

"[email protected] [domaindrivendesign]" <[email protected]> 28 Nov 2014 06:10:31 -0800

Newsgroups	gmane.comp.programming.domain-driven-design
Message-ID	<[email protected]>

I'm stuck at a quote from  Vaughn Vernon in his IDDD book. Here it goes:
 

 "An Aggregate is composed of either a single Entity (5) or a cluster of Entities and Value Objects (6) that must remain transactionally consistent throughout the Aggregate’s lifetime." - Implementing DDD by  Vaughn Vernon
 

 I'm trying to understand "transactionally consistent" that is mentioned here. Is it the behavior of the repository that makes sure the aggregate should be consistent when it is read or committed from the database.
 

 Or it the consistency of the aggregate when it is operated in memory and goes through state changes and shows consistent behavior.