I forgot the name, but I remember reading about it in lifehacker or i09 some time ago.
When the group feels a certain way, but say that they feel the other way to avoid being the only one to agree. Despite all of them feeling the same way.
For example, a group goes to a restaurant. All of them hate the food. But no one wants to be the one to say it, so they all unwittingly say it's great and that they are enjoying.