Production
Production is a general term for the two client-facing environments we work with during development: live and staging. Our live and staging environments share the same set of theme code because they are both on the production servers. Usually, you'll hear this in terms of where we need to deploy code or when code is "ready" to go somewhere. Ready for production means code is ready for prime time: it's been tested extensively, verified, and you're ready for it to go in front of clients and end users.
It's important to know that live and staging share code on production because if you have an existing live site and that same theme is being used on a staging site, the deploy process for that theme has to be modified slightly to prevent changes from showing on the live site. If you are in this situation, consult a developer before you begin development work to figure out the best workflow for your project.