I think you mean what is COP, COP is Client Operations Profiles.
COP determines who goes where for what agent-wise along with any specific agent settings.
A SAP is a Server Access Profile which defines a "server" (an item of RCA infrastructure) and it's abilities, in other words what it can offer to an agent.
Each "server", i.e. Core or Satellite in the environment has a number of things it can offer to an agent. Cores and Full Satellites can offer a client it's desired state information (CONFIG) and/or the resources to perform an installation (DATA), Streamlined Satellites can only offer DATA, these capabilities are configured as SAP entries.
There is a concept of a LOCATION which consists of a number of SUBNETS. LOCATIONS are connected to a number of SAPS which can also be prioritised.
Using this setup you can determine which pieces of infrastructure an agent will talk to based upon its location (i.e. its subnet). This is how you build your RCA infrastructure.
Once an agent connects into RCA it receives its configured list of infrastructure which is then stored locally in the SAP.EDM object, this is known as a COP connect and controlled via COP=Y/N on the command line.
There's much more to it than the above and there are many other things you can control with COP but that's a quick explanation.