Secondary suite is what used to be called a Mother in law suite right?

I've never heard of this rule, can you expand on it please? Reason why? Which province(s)? Does it only apply if you rent it out?

Technically, I guess this is what we have but we don't rent it out and there's no separate entrance to it. It actually works wonderfully for us as I use it solely for daycare purposes. When we move to a bigger home, this is actually a must have for me now that I've been spoiled by having it!