The agent is online and will accept tasks for execution when it has free executors.
The agent has been explicitly set to temporarily offline by a user. If the agent is still connected any running tasks will finish. No new tasks will start until the agent is put online again by a user.
The agent is not accepting tasks for execution. This usually means that the agents availability settings prevent task execution, e.g. when using Bring this agent online according to a schedule and being outside the time window. The agent might still execute tasks that have started while it was accepting tasks. Cloud agents that are intended to run only a single task might also use this. Agents will be shown as suspended in the Build Executor Status widgets.
None of the above conditions applies. The agent is not connected or it is still connected but a node monitor decided that the agent is not in a healthy state. An agent in this state should be investigated.