Instead of having one common set of build agents, you can break them into separate groups called agent pools. A pool is a named set of agents to which you can assign projects.
An agent can belong to one pool only.
A project can use several pools for its builds.
The number of agents authorized by the TeamCity server is limited by the number of agent licenses. By default, all newly authorized agents are included into the Default pool.
With the help of agent pools you can bind specific agents to specific projects. Project builds can be run only on build agents from the pools assigned to the project. Agent pools can also help to calculate the required agents' capacity.
You can find all agent pools configured in TeamCity on the Agents | Pools tab.