Development and deployment on Force.com typically takes place in an environment or org, which provides a number of features and services for applications within that environment. An environment lets you instantly start developing, testing and deploying your app in the cloud. For an explanation of the types of environments, see An Introduction to Environments.
Developer Edition (often referred to as a "DE org") is a fully-featured development environment with limits on data and users. Developer Edition is used for:
When you're ready to begin developing, you'll find that Developer Edition is equipped the full Salesforce CRM suite, along with all the latest developer technologies. Sign up for a Developer Edition and you'll get your new environment provisioned immediately. Note that Developer Edition orgs continue to be available as long as they have some type of activity within the previous six months.
For a full side-by-side comparison between Developer Edition and other Salesforce editions, see Salesforce Feature and Edition Limits.