Support Skills are those skills which affect how well you can fit/use/fly ships and modules, without being skills directly required to use the modules or enter the ships. Common examples are capacitor-related skills such as Energy Systems Management, and fitting skills such as Advanced Weapons Upgrades.
Since 'good support skills' is a cliché in the Uni and EvE generally, this page attempts to define the skill set and suggest what levels qualify as good in what circumstances. Wish us luck.