The reply is the Crown's responding pleading in a Tax Court of Canada appeal, filed by Department of Justice counsel for the Minister of National Revenue. It admits or denies the facts pleaded in the notice of appeal, states the Crown's position and the statutory basis for the reassessment, and sets out the assumptions of fact the Minister relied on at reassessment.
The reply is often the most consequential document in an appeal, because the assumptions of fact it pleads are presumed true unless the taxpayer rebuts them. Reading the reply closely tells the taxpayer exactly what must be proved, which is why the case theory is built around it.