Canvas enables you to easily integrate a third-party application in Salesforce. Canvas is a set of tools and JavaScript APIs that you can use to expose an application as a canvas app. This means you can take your new or existing applications and make them available to your users as part of their Salesforce experience.


Canvas App Previewer
Canvas App Previewer is a development tool that lets you see what your canvas apps will look like before you publish them.

The third-party app that you want to expose as a canvas app can be written in any language. The only requirement is that the app has a secure URL (HTTPS).

apex:canvasApp is the tag to use in Visualforce page.