Deploy
To deploy is to put the newest version of your site online, where visitors can see it.
In a simple example
You finish a change, press Deploy, and a few minutes later the new menu is live.
Why it matters to you
Until you deploy, your changes exist only for you. Deploying is the moment the world sees them.
Do not confuse with
Deploy is not the same as merge. Merge joins code. Deploy publishes it.