Component based vs full stack framework?

I don't understand what these 2 words mean.

I think symfony is a开发者_运维知识库 full-stack framework while yii is a component-based framework.

Is this correct?

If so, what are the main differences?

full-stack frameworks (symfony) you use the entire stack.

component frameworks (zend) you pick and choose what libraries you want.

Component framework may also refer to visual components as in Widgets.