Short answer. Section 4 of Rule 6 defines the answer simply as 'a pleading in which a defending party sets forth his or her defenses.' It's the formal, written vehicle by which the defendant responds to the claims made against them in the complaint.
What the law says
An answer is a pleading in which a defending party sets forth his or her defenses.
Rule 6, Section 4 — Answer. Read the full provision →
The core definition
Section 4's definition is deliberately brief: an answer is the pleading where a defending party sets forth their defenses. This positions the answer as the direct counterpart to the complaint defined in the preceding section — where the complaint states the plaintiff's claims, the answer states the defendant's response to those claims, completing the basic claim-and-response structure that frames most ordinary civil litigation from the outset.
What 'defenses' can include
The word 'defenses' here is broad, and the immediately following section of Rule 6 fleshes it out further by distinguishing negative defenses (specific denials of the plaintiff's factual allegations) from affirmative defenses (new matter that would defeat the claim even if the plaintiff's allegations were true). An answer is where both types find their place, giving the defending party the vehicle to contest the plaintiff's factual claims and to raise independent grounds for defeating the action.
Why the answer matters procedurally
Because the answer is the defendant's formal, on-the-record response, what it does or does not say has consequences for the rest of the case — allegations not specifically denied may be deemed admitted, and defenses not raised may later be considered waived. This is why the Rules devote considerable additional detail, in subsequent sections and rules, to exactly how denials and defenses in an answer must be framed.
Who besides the original defendant can file one
The definition refers broadly to a 'defending party,' not narrowly to the original defendant alone, which is why the same basic concept of an answer also applies to a third-party defendant responding to a third-party complaint, or a defendant in a counterclaim responding to that counterclaim. Anyone occupying the defending role in a given claim files an answer to set forth their defenses to that specific claim, whatever their formal position elsewhere in the case. None of this changes what happens if no answer is ever filed at all; a defending party who fails to set forth any defenses within the period allowed risks being declared in default, which is precisely why Section 4's definition of the answer as the vehicle for defenses carries real practical weight rather than being a purely descriptive label. Understanding what belongs in the answer is therefore the first step toward avoiding that consequence.