However, there are some disagreements as to what exactly that means.
For some people it includes a fic that isn't focused on the romance, but where pairings can feature in the background. Some people make a difference between showing canonical pairings and non canonical pairings (with all the debates that can lead to about what's a canonical pairing), which many slashers criticize as being hetero-sexist, because the majority of what's acknowledged as canonical pairings do not include their ships.
It's sometimes used to mean an Original Flavour fic.
Beyond what it doesn't include, Gen's a category for plot-focused stories or light day-in-the-life stories. It's often popular among fans who like to explore all the dynamics of the ensemble cast, to put the focus more on the family and the friendly relationships.