With lazy consensus the idea is that a potential contributor notifies the community of their intentions. For example, they may say "I intend to do XYZ, unless someone objects within 3 days I will go ahead with this." This notification can be made in any form that the community accepts, such as via a mailing list or a shared document space with community notification devices (or in non-technical speak, a village noticeboard ;-) ).
The benefits of this approach include the fact that in the absence of an objection one can assume one has consensus. Community members with no objection and nothing to add to the contribution need take no action. Only those people who believe they can help improve it or those who believe there is a flaw in it need spend any time contributing or objecting to the proposal.
A further advantage of Lazy Consensus is perhaps the most important. Lazy Conensus removes the risk of slipping into despotism since community consensus is still required. No contribution is made without the implicit approval of the community and so nobody can cry "foul" at a later date.
From: Ross Gardler on OSS Watch