The framework this house builds its interfaces in. A named tool rather than a concept.
Italian svelto (slim, quick, nimble), the past participle of svellere (to pluck out), from Latin evellere (to pull out); the framework borrowed a word for something made lighter by having the unnecessary pulled out of it.
The framework this house builds its interfaces in, named for slimness bought by removal rather than by cleverness added on. What is not needed at runtime is pulled out before a page is ever sent.