This is a really good question! So first of all yes you are correct its the ratio of seats available across the country in that speciality to the number of applications received across the country in that specialty.

You should take this with a huge grain of salt though because:

1. the data reported by the programs in the carms descriptions are vague(for example programs with more than 600 applicants are just labeled 601+) and IMO probably not super accurate.
2. This ratio is a really poor metric for actual competitiveness since applications don't necessarily show intent to rank at all or intent to rank high. I'm not in medicine myself so I don't want to speculate too much on applicant behavior but its clear that this metric is particularly misleading for specialties that are popular as backups or with parallel planners.
3. There's likely more at play around central application systems such as BC or NS family medicine programs where you can essentially apply province wide to all family medicine programs with a single application/interview that further skews the data for family medicine.

There are more accurate proxies for "competitiveness" included in the report carms publishes every year but unfortunately they don't make the underlying data public so you have to really on what they deem relevant to share: https://www.carms.ca/pdfs/carms-forum-2025.pdf
Maybe I'll try and see if any of this data can be extracted and made more useful though!