Which term best describes a reply to a criticism or an objection?

The term that best describes a reply to a criticism or an objection is "rebuttal." A rebuttal is specifically designed to counter or refute a point made by an adversary, typically in a debate or argument. It highlights the speaker's or writer’s position against the criticism and provides reasoning, evidence, or arguments to challenge the validity of the objection.

In a debate context, a rebuttal serves to clarify misunderstandings, present alternative interpretations, or outright deny the claims made by the critic, thus strengthening one’s argument. This active engagement in dispute aligns well with the essence of addressing criticisms, which is why "rebuttal" is the most precise term among the given options.

On the other hand, the other terms do not accurately capture the active response to criticism. A contradiction refers to directly opposing a statement, corroboration involves supporting or confirming a claim rather than countering it, and affirmation signifies agreement or validation, which does not pertain to addressing criticism.