Consensus normally means that a decision is taken almost unanimously, with no-one voicing dissent. Consensus over a proposal can thus be reached without total backing, as long as no-one openly declares their opposition.
In the European Council consensus has so far been the procedure for reaching decisions. In this forum consensus means that no Heads of State or Government voice opposition. The former EU treaties do not mention this procedure.
The Lisbon Treaty formally introducing 'consensus' as the most important decision-making procedure in the European Council.
During the Convention on the Future of Europe, 'consensus' was used in a new manner more reminiscient of a qualified majority. The convention procedure was criticised becauce the President, Giscard d'Estaing, was not always in line with the general majority when deciding what the consensus was.
Decisions supported by 90 percent of the members were left out of the proposals for the EU Constitution, whereas others with poor support were included.