How Merge Replication Works
Merge replication supports bidirectional subscriptions, with changes propagated from the subscribers to the publisher. 

Other types of replication support this scenario: Transational Replication with updateable subscriptions (deprecated) and Peer-To-Peer Transactional Replication (more complicated to maintain, requires Enterprise Edition).

Keep in mind that Merge Replication keeps track of changes using triggers on each published table (article), which can determine substantial overhead to all write operations against those tables. Merge Replication also requires a unique uniqueidentifier column on each article: if you don't have one, it wil add it for you (more space needes, heavy fragmentation after adding the column). 

Make sure you test performance before going down this road.