I'll elaborate on what Richard & Chris said -
Replication is a set of technologies
for copying and distributing data and
database objects from one database to
another and then synchronizing between
databases to maintain consistency.
Using replication, you can distribute
data to different locations and to
remote or mobile users over local and
wide area networks, dial-up
connections, wireless connections, and
the Internet.
Transactional replication is typically
used in server-to-server scenarios
that require high throughput,
including: improving scalability and
availability; data warehousing and
reporting; integrating data from
multiple sites; integrating
heterogeneous data; and offloading
batch processing. Merge replication is
primarily designed for mobile
applications or distributed server
applications that have possible data
conflicts. Common scenarios include:
exchanging data with mobile users;
consumer point of sale (POS)
applications; and integration of data
from multiple sites. Snapshot
replication is used to provide the
initial data set for transactional and
merge replication; it can also be used
when complete refreshes of data are
appropriate. With these three types of
replication, SQL Server provides a
powerful and flexible system for
synchronizing data across your
enterprise.
In addition to replication, in SQL
Server 2008, you can sychronize
databases by using Microsoft Sync Framework and Sync Services for
ADO.NET. Sync Services for ADO.NET
provides an intuitive and flexible API
that you can use to build applications
that target offline and collaboration
scenarios.