Integration refers to the work that is done on other systems or Salesforce to enable them to communicate with each other. There are different layers of integration in Salesforce: security, UI, logic, and data and there are many different mechanisms for integrating, including 3rd party apps.
Itegration refers to the work that is done on other systems or Salesforce to enable them to communicate with each other. There are different layers of integration in Salesforce: security, UI, logic, and data and there are many different integration patterns and approaches, that can may be implemented on either of the integrated systems or through a middleware platform, a great resource for salesforce specific integration is the Salesforce Integration Patterns and Practices - Dev Guide.
