Learning Tools Interoperability® (LTI®) is a specification developed by IMS Global Learning Consortium. It establishes a standard way of integrating rich learning applications, called tools (delivered by tool providers) with platforms such as learning management systems, called tool consumers.
Moodle as a LTI tool consumer
In Moodle 2.2 onwards, the External tool enables users to interact with LTI-compliant learning resources and activities on other websites.
Moodle as a LTI tool provider
In Moodle 3.1 onwards, the Publish as LTI tool enrolment plugin and LTI authentication plugin allow remote users on a different site to access selected courses and activities on your site. When these users access an activity on your site, they need an account on your site and they need to be enrolled in the course containing the activity. Thus, an enrolment plugin AND an authentication plugin are required for LTI tool provider functionality.