According to C.S. Lakin (whom I adore) universal appeal means that a whole bunch of people all over the world should be able to relate to our novel, perhaps in any time in history.
In her post called 'Universality is in the Details' Lakin gives some great advice on a few ways we can easily create a broader appeal in our writing.
on’t make the mistake in thinking that in order to appeal to a wide audience with a universal appeal we have to write in very general terms and details. You may think that the more specific you can get with your locale, setting, time period, problems presented, the more universal the novel will be. You may think if your character can have a general problem—say a bad temper or he’s a Scrooge—a lot of people will identify with him . . . so you decide to not be too specific and take the risk of making your novel’s world so small that no one will relate."
Lakin goes on to explain that 'general is not universal.' Many authors are worried if they focus on a certain time or place, their novel will soon become outdated. She says this is simply not the case.
She points out that the powerful novels, the classics, that have stood the test of time zoomed in on a tiny moment in time in a very specific place.
Lakin says the key to making our work believable and appealing is in the details, and encourages writers to no shy away from being very specific in our scenes. We should think like a journalist, finding details that add credibility and believability to our stories.
"Believability is the key to universality," Lakin says.
Read her full post here, including an excerpt of an interview from Gabriel Garcia Marquez.
I've heard it said that beauty is in the details. It seems that believability lies there, too.