This is a difficult question to answer because its seminal document didn’t call it that, and the secular and Church versions have diverged over time.
In Pope Leo XIII’s encyclical “Rerum Novarum” he greatly encouraged the idea of wide ownership of productive, inheritable assets. In his day, that pretty much meant farm land. He supported that because, he taught, it was conducive to the freedom of individuals and families to adopt the moralities of religion as opposed to the ideologies of consumerism or government. Later writers like Chesterton, Belloc and Lewis expanded that to include small shops and manufactories. The views of the secular writers later took on a sort of collectivist overlay that was very much a departure from the teachings of Pope Leo XIII.
Later Popes wrote about the same thing, but noted the change in economies from the widespread small farm model, and said it would need to take on different forms today. But never did they ever really call it “distributism”. Nor did they embrace the collectivst or cooperative model that the successors of Chesterton, Belloc and Lewis embraced.
So, there are a lot of versions of what “Distributism” is, most of them at odds with the original encyclical that can be said to have given birth to it.
So, if we want to think of it in terms of the Social Encyclicals, we need to think about the main principles and see how they can have application in our own lives.
First, rejection of consumerism inasmuch as it’s possible to do it. Excessive consumerism tightens the grip employers, particularly large ones, have on us. It causes us to be cogs in a wheel of work and consumption that we can’t easily escape.
Second, and coupled with the first, investment of family resources in productive assets. This will vary tremendously from person to person. For one it might indeed be land. For another it might be renovating houses on the side. For another it might be a 401K. But always there are the characteristics of ownership, productivity and inheritability. A quite smallish example I can cite is a young woman i know who works at a regular job, but has saved her money to buy a tractor, a tedder and a baler. She does custom work for farmers with her own equipment on weekends and long summer evenings. Those modest assets are productive, she owns them, and they’re inheritable. The more she does what she does, the more she will acquire and the more independent she will become.
Nowadays, except in a few commune-like communities, that’s what it is. It’s more conceptual and personal than it is an external system.