Family resemblance is the idea that some concepts are defined by a set of overlapping traits rather than a single definition. The term is most famously associated with Ludwig Wittgenstein, though the idea did not originate with him.
In Philosophical Investigations Wittgenstein asks readers to consider the concept of games. He notes that there is no single trait that is shared by all games. The category of game includes things as diverse as:
Baseball
Poker
Dungeons & Dragons
Scrabble
Fortnite
Hide and seek
400-meter hurdles
There is no single thing that unifies all these activities, though many share some sets of similarities. As Wittgenstein puts the point:
We can see how similarities crop up and disappear. And the result of this examination is: we see a complicated network of similarities overlapping and criss-crossing.
In the years since, I've written on a number of topics around writing and publishing text on the web. Like TCF's erstwhile research program, my writing has lacked a single through line. But there is perhaps something of a family resemblance. Most things connect to at least some other things, though rarely in a way that builds a single, sustained argument.