A more thorough explanation:

Unilateral

Unilateral means something that is one-sided or done by only one party without the agreement or participation of others.

• When the United States imposed a unilateral trade embargo on Cuba, it meant that the US stopped trading with Cuba, but Cuba did not agree to stop trading with the US.
• When a person decides to end a friendship unilaterally, it means that they are ending the friendship without the agreement or participation of the other person.

These examples illustrate the definition of unilateral because in both cases, one party is taking action without the agreement or participation of the other party. In the first example, the US is imposing a trade embargo on Cuba without Cuba's agreement. In the second example, one person is ending a friendship without the other person's agreement or participation.