社会generally means society, community.
But what is its real meaning in the following cases: 1. 社会力量办学；2.此为公交专用车道，社会车辆不得驶入; 3.走出校门，走进社会？
My understanding is: 1. schools run by private sector; 2. this is the track for public transportation only, private traffic is denied. So 社会 means private?
As for No. 3, I think it means I leave the school and enter the society, but isn't school part of the society?