The Applicant Support Form or a Lettre d'appui (or Formulaire d'appui) are a type of referee evaluation form consisting of check boxes for them to fill out and submit. The forms themselves are generally provided in the program descriptions. Applicants must fill out some of the information before giving it to the referee to provide the rest and submit it.
In addition, you must create a reference request for them the same way you would request a reference letter in CaRMS Online. The difference is that you can select "Applicant Support Form" as the "Reference Document" when completing the request. You will need to give your referee the form so they can submit it accordingly.
Some programs in Québec for the R-1 match are requesting a standardized "lettre d'appui / formulaire d'appui" (the same form is used across disciplines and universities, the link available in the program description). This is with the exception of R-1 Dermatology programs in Québec, that have their own Dermatology applicant support form.
Additionally, the R-1 University of Manitoba / Anesthesiology program requests their own applicant support form.
Note: this is not a definite list of programs that require these forms. You must review program descriptions of programs you're applying to, to ensure you're submitting the correct reference documents.