What is a merit brief?

A "brief" is a paper filed with the court for the court's use (usually in a case under consideration). Accordingly - the following of definition of legal "merit" will be self-explanatory.

"Merit is a term subject to various meanings, but in the legal context, merit refers to a claim which has a valid basis, setting forth sufficient facts from which the court could find a valid claim of deprivation of a legal right. Meritorious claims usually cite legal authorities, such as statutory laws or case law, to support their arguments. However, merit is a subjective term that takes various factors into account on a case-by-case basis. For example, a pro se defendant seeking post-conviction relief is often be expected to construct legal arguments, cite legal authority, or draft her petition as artfully as a lawyer would. If the evidence defeats the claim, the claim is "meritless."