The workflow definition contains the actual business logic that is defined as part of the Logic Apps built. Workflow definition language is described thoroughly over Microsoft documentation: https://docs.microsoft.com/en-us/rest/api/logic/definition-language.

The basic structure of workflow definition Language is as follows:

{ 
      "$schema": "<schema-of the-definition>", 
      "contentVersion": "<version-number-of-definition>", 
      "parameters": { <parameter-definitions-of-definition> }, 
      "triggers": [ { <definition-of-flow-triggers> } ], 
      "actions": [ { <definition-of-flow-actions> } ], 
      "outputs": { <output-of-definition> }     
}