Once the design and implementation of the site is completed, it is ready to be launched.
The deployment of the site generally involves moving the site from the development environment to the production environment. On a new site this might only involve adding the analytical piece and publishing the site to the search engines, while on a refreshed site this involves the moving of the site physically from the development platform to the production platform.
Often there are technical issues involved in migrating a site, involving the use of a new hosting provider or configuration changes on the host that are needed to support the site.
While the deployment of a new site may simply be turning on the new site, more often than not this event is built into a marketing, PR or other promotional opportunity. Customers like to see new developments at a company since it means growth and development and can allay fears of negative aspects of a troubled economy.