A package is a container for something as small as an individual component or as large as a set of related apps. After you create a package, you can distribute it to other Salesforce.com users and organizations, including those outside your company. An organization can create a single managed package that can be downloaded and installed by many different organizations. They differ from unmanaged packages in that some components are locked, allowing the managed package to be upgraded later. Unmanaged packages do not include locked components and cannot be upgraded.
This section includes the following topics related to developing Apex in managed packages: