According to the Lightning Web Components Developer Guide, Lightning Out is a technique that allows developers to run Lightning web components outside of Salesforce servers, such asin a Node.js app running on Heroku or a department server inside the firewall. Lightning Out uses a script tag to load the Lightning web components framework and the custom components into the web container. Lightning Out also handles authentication, eventhandling, and data access between the web container and the Salesforce org. Slot elements, Heroku, and Lightning Canvas are not techniques for exposing Lightning web components outside of an org in another web container. References: Lightning Web Components Developer Guide, Use Components Outside Salesforce, B2B Commerce and D2C Commerce Developer Guide