Digital gardens are note systems (usually published ones although some people talk about private digital gardens but to me that’s just notes) where instead of sequential publishing, authors publish their ever-evolving notes on topics they are interested in.
In my case here, this digital garden is my Obsidian vault that I use while working on this year’s Advent of Code puzzles.
If you want to learn more about digital gardens, I can recommend Maggie Appleton’s A Brief History & Ethos of the Digital Garden and swyx’s Digital Garden Terms of Service.