Phtamas, thank you that is going be a good start for me. And basically that seems to be what I needed to hear.
Others, thanks for the comments!
Just to clear this up:
Yii is a framework which would allow you to build WP, phpbb or whatever. A framework is just really a set of libraries that help you instead of redoing everything for the beginning again.
So you are right comparing Yii to WP is impossible. Comparing Yii to drupal is also not correct. However comparing to symfony, CI, fuel, lithium or cakephp is possible. But I would not compare Yii to silex or any other "lite" framework because they server different purposes and the amount is loaded for you is completely different.
Because Yii is a framework it also has made decisions for you which sometimes are just awesome and sometimes will suck! It is all a trade off.
You should just learn it! And then you’ll understand how to answer the questions yourself.
Imagine if your teachers at school told you that 
Imagine if a store told you to study all the specs before you before you bought your next pc 
Sometimes it is just easier to ask questions than to spend a lot of time googling. I googled a lot before I posted my question, I spent time looking first but if you are not familar to a projects "terminology" then it really is hard to know what you are looking for.
Module, extension, plugin, widget, snippet, and what not can mean different things to different projects. If you don’t ask how can you learn?
I came here because I want to port my 16mb MVC project to a heavier framework. sF2 or zend are my only other choices. All the other frameworks don’t really compare to Yii, sF2 or zend. Although Yii is slightly lighter thand sF2 or zend I am thinking that with Yii2 that I’ll be able to have the best of both worlds.
Has anybody come across a Yii project that has imemented plugins like WP does?