General term for an RPG system intended for multiple settings. The difference between a "universal system" (like GURPS) and a "house system" (like Storyteller) is largely one of publishing -- i.e. do you publish core rules and then modifications to those, or do you publish tailored rule sets with the modifications already applied? This can be a controversial topic on The Forge, which only goes to show that any trivial thing can be a controversial topic on the Forge.

References:

• universal vs specific systems
• General views on Universal systems?