الشعب يريد أسقط النظام

It mean "The people want the collapse of the regime"

You can hear it chanted loudly from every video from across Syria.
Here is a good video or two

Libya

Syria
Shouting Freedom, Freedom, Freedom and God is the greatest
By blood, and soul we will give our lives, yeah martyrs

The people want the fall of the regime


Another Video with a good overview so far in English