Igor Wiedler has shared some of his thoughts on his site today about the "heaviness" of things that call themselves "microframeworks" and why it may not be about the amount of code involved at all.
Quite often silex has been described as heavy or bloated. It's time to put this myth to rest. [...] Micro-framework What an excellent buzzword! Let's face it, this is an overloaded and mostly nebulous term. I don't think it's possible to clearly define what it means. [...] But the real answer lies in what silex doesn't do.
He suggests that the "micro" in "microframework" is more about it providing a limited amount of features (bare-bones) versus a more full-featured, possibly full stack framework. He talks about the dependencies that Silex currently has and provides some statistics about it and these packages it depends on. He also briefly mentions the minimal interface the framework provides, citing the few components you'll probably touch in your work with it.