Publisher

The Publisher is a server that makes data available for replication to other servers. In addition to being the server where you specify which data is to be replicated, the Publisher also detects which data has changed and maintains information about all publications at that site. Usually, any data element that is replicated has a single Publisher, even if it may be updated by several Subscribers or republished by a Subscriber. The publication database is the database on the Publisher that is the source of data and database objects to be replicated. Each database used in replication must be enabled as a publication database either through the Configure Publishing and Distribution Wizard, the Publisher and Distributor properties, by using thesp_replicationdboption system stored procedure, or by creating a publication on that database using the Create Publication Wizard.

Distributor

The Distributor is a server that contains the distribution database and stores meta data, history data, and/or transactions. The Distributor can be a separate server from the Publisher (remote Distributor), or it can be the same server as the Publisher (local Distributor). The role of the Distributor varies depending on which type of replication you implement, and in general, its role is much greater for snapshot replication and transactional replication than it is for merge replication. 

Subscribers

are servers that receive replicated data. Subscribers subscribe to publications, not to individual articles within a publication, and they subscribe only to the publications that they need, not necessarily all of the publications available on a Publisher. If you have applications using transactional replication built with Microsoft® SQL Server™ version 6.5 or later, and those applications subscribe directly to articles instead of to publications, the applications will continue to work in SQL Server 2000. However, you should begin to migrate your subscriptions to the publication level where each publication is composed of one or more articles.