What do you install when you want to add applications or functionality within your development instance?

A Patch is an update to fix bugs or introduce minor improvements to existing functionality, not to add new applications.

Updated Pack is not a standard ServiceNow term for adding new applications.

While functionality comes in "packages," "Plugin" is the specific ServiceNow term for activating new features.

Plugins in ServiceNow are packages that add new features, applications, or integrations to an instance. When you want to introduce new functionality, such as a new IT Service Management application or a specific feature like Knowledge Management, you typically activate the corresponding plugin in your development instance.

An Update Set is used to transfer configurations between instances, not to install new applications or functionality from the store.