In Pennsylvania, an Affidavit of Defense is a legal document a defendant files in response to a civil lawsuit, typically in cases involving a writ of scire facias or similar actions where a default judgment can be entered if no defense is presented. This affidavit must set forth a positive ground of defense on the merits of the case and be made by the defendant or someone with knowledge of the facts. 

Rule 206.2. Answer. (a) An answer shall state the material facts which constitute the defense to the petition. (b) An answer to a petition shall be divided into paragraphs, numbered consecutively, corresponding to the numbered paragraphs of the petition. Source The provisions of this Rule 206.2 adopted September 8, 1995, effective January 1, 1996, 25 Pa.B. 4092