In Jenkins, an agent and a node are similar concepts, but they are not exactly the same thing.
An agent is a term used in the context of the Jenkins pipeline. It refers to a machine or a container on which a pipeline runs. In a pipeline, you define which agent should be used to execute each stage or task of the pipeline.
On the other hand, a node is a term used in the context of the Jenkins master-slave architecture. In this architecture, the Jenkins master controls one or more Jenkins nodes (or slaves), which are separate machines that can be used to distribute the workload of running jobs. Each node can be assigned specific labels, which can be used to restrict which jobs are allowed to run on that node.
So, in summary, an agent is a concept used specifically in the context of a Jenkins pipeline, while a node is a concept used in the broader Jenkins master-slave architecture. However, in practice, the terms are sometimes used interchangeably.