The association between a command and the key combinations that should invoke the command is called a key binding. Plug-ins can define key bindings along with commands in the org.eclipse.ui.bindings extension point.
... <key commandId="org.eclipse.ui.file.save" contextId="org.eclipse.ui.contexts.window" schemeId="org.eclipse.ui.examples.contributions.scheme" sequence="CTRL+S"> </key> ...
There is our friend org.eclipse.ui.file.save. In Eclipse, the workbench registers the SaveAction as a handler for this command id in every Workbench Window.
The sequence attribute for a key binding defines the key combination that is used to invoke a command. When the workbench SaveAction is active, the key combination CTRL+S will invoke it, since the workbench uses the same command id for its SaveAction.