Unilateral means "one-sided." If parents make a unilateral decision to eliminate summer vacation, it means that the students’ opinions or opposing views weren’t considered.
When someone makes a unilateral decision, he or she acts alone, without considering the feelings, opposing opinions or concerns of others. But it’s not always a bad thing to act unilaterally. If you are in a fight with your sister and haven’t spoken to each other for a week, you could choose to do her chores, compliment her or make other unilateral, good-faith efforts to bring the bad feelings to an end.