My understanding is that, this means to (illogically) say that something is right because that is the way it has always been. Other times I’ve seen it said that this fallacy can also encompass the fallacy that something should change because it has been a certain way for a long time (although it still works (also known as fixing something that isn’t broken)). However, the first definition is the way it is usually understood.
So a person might have fixed ideas about the way a good date should go, the kind of normal places you should go (the cinema rather than tomahawk throwing) and that the man pays for everything and holds the door open for the lady blah blah blah. There are also traditional ways to meet people, through dating apps or matchmaking or whatever, but because that’s the way it’s always been done, it would be illogical to discount any other ways because of this ‘tradition’ i.e. long-standing norm.