Azure Pipelines Agents - Azure Pipelines
Note In Microsoft Team Foundation Server (TFS) 2018 and previous versions, run and release pipelines are called definitions, runs are called builds, service connections are called service endpoints, stages are called environments, and jobs are called phases. To build your code or deploy your software using Azure Pipelines, you need at least one agent.
https://docs.microsoft.com/en-us/azure/devops/pipelines/agents/agents?view=azure-devops&tabs=browser#communication