A more thorough explanation:

AVER

aver (uh-vur), verb. To confidently state something as true, especially in a legal context.

• The lawyer will aver that his client is innocent of the crime.
• The witness will aver that she saw the defendant at the scene of the crime.

These examples show how aver is used in a legal context. When someone avers, they are making a strong statement that they believe to be true. In a court case, for example, a lawyer might aver that their client is innocent, meaning they are stating it as a fact. Similarly, a witness might aver that they saw the defendant at the scene of the crime, meaning they are asserting it as true.