sc is a command line utility that manages windows service entries. The command in this case works by deleting the service entry that is left over by the previous version parallels tools uninstaller. When the newer version of parallels tools installs, it does not properly install the coherence service if there is already an entry for it in the list of windows services. Coherence must be installed (as a windows service) in order for it to work. By deleting the service you allow the newer version installer to install the new coherence service as intended.
More basically, services are programs that can run (usually in the background without interaction) regardless of which user is logged in. You can see which services are running, when they are configured to start and which credentials they are running under using the services mmc snapin (run mmc, add/remove snapin, choose services). Or you can right click on My Computer, select manage and expand the Services tree.
Last edited: Dec 22, 2006