Collective Rule is a social policy in Civilization V. It is part of the Liberty tree. In the expansions, it requires Republic; in Vanilla, it is instead initially available and actually was a prerequisite for Republic.
Giving people the right to vote and decide the matters governing their life, instead of, say, a single despot doing whatever he decides, is the first step towards freedom. So important is this step that the Capital of your empire becomes a brewing pot of expansionism, and people are ready to establish new cities right away!
- Speeds the training of Settlers by 50% in the Capital.
- A free Settler appears near the Capital. (Venice receives a Merchant of Venice instead of a Settler.)
With the expansions, this policy is level 2. But still, if you rush it and adopt it as a third policy you will gain a free Settler without having the need to sacrifice Population growth in your starting city in the all-important first 20-30 turns. Building a Settler at that point usually takes 10+ turns, which makes this Policy a game changer - you not only will continue to grow your Population, but also manage to construct something else in this time! And of course, the other bonus will greatly facilitate future expansion.
Collective rule is the policy in which every member (or every adult member, or every adult male member) of the society takes part in the governing process, voting directly upon decisions rather than through a representative (as in a republic). While perhaps an effective form of government for tribes or small villages, collective rule becomes increasingly more difficult and unwieldy as the polity increases in size. If half of the citizens of a tribe of 100 each wanted to speak for one minute at a meeting, they could do so in under an hour. If half of the citizens of New York City each wanted to speak for one minute, they would need some 66,000 hours (plus a really huge meeting hall).