In Canada , it's the French brand-name for RubA535, a "warming" friction rub for sore muscles that contains methyl salyciate (a cousin of Asprin) which soothes skin and also irritates it, producing a feeling of "heat" which distracts the brain from the other pain- the muscle soreness. It's very popular with long-distance runners.

However, I have to be picky and complain that I wouldn't call it a "poultice". It only gives the impression of heat- it doesn't use real heat to cure. A poultice is a mix of something that really is hot (or cold), which is applied to the skin to give real heat(or cold) to the body, and this reduce discomfort and swelling. A hot water bottle is, in fact, a poultice. Since we are on the subject, Canadian hospitals have been known to use hot bran poultices to relieve the trauma and discomfort resulting from a Caesarian section... to which I can personally attest. And, for the record, that was in English Canada, not French Canada. Quebec Health Care, which I have also experienced, really doesn't encourage old-fashioned stuff like poultices and breastfeeding. Which doesn't mean that you don't get good care there...you do.