They mean a dispatcher. In a multi-server environment, you may have your content manager and your dispatcher(s) in separate installs.
Here's the official definition:
The IBMCognos 8 applications tier contains one or more IBM Cognos 8 servers.
An IBM Cognos 8 server runs requests, such as reports, analyses, and queries,
that are forwarded by a gateway. An IBM Cognos 8 server also renders the IBM
Cognos Connection and studio interfaces.