Agreement by 100% of the people involved.
The adoption of legislative proposals in certain areas of EU policy requires that that there is unanimity amongst the Member States in the Council. Such cases provide the exception under the First Pillar while under the Second and Third Pillars where policy is conducted along intergovernmental lines unanimity is the norm.
Unanimity is complete agreement by everyone. When unanimous, everybody is of same mind and acting together as an undiversified whole. Many groups consider unanimous decisions a sign of agreement, solidarity, and unity.