There are two types of Standalone Updates: Individual and Combo.
Individual Updates update one version of Mac OS X to the subsequent version. For example, the Mac OS X 10.2.4 Update updates Mac OS X 10.2.3 to version 10.2.4. Individual Updates are also known as Delta Updates.
Combo Updates update the base version of a Mac OS X release to the version specified in the Combo Update, including all intermediate updates. For example, the Mac OS X 10.2.4 Combo Update updates:
Mac OS X 10.2 to Mac OS X 10.2.4 with one installation, as opposed to installing the individual Mac OS X 10.2.1, 10.2.2, 10.2.3, and 10.2.4 updates.
Mac OS X 10.2.2 to Mac OS X 10.2.4 without installing the individual Mac OS X 10.2.3 and Mac OS X 10.2.4 updates.
Standalone Updates are generally available 24 to 48 hours after the corresponding Update is available through Software Update.