Domain knowledge, in a nutshell, is knowledge about a specific industry or a even more specific part of an industry.
In the context of software development, of what use is domain knowledge? Domain knowledge is an undervalued part of any successful software development project. The programmers at the keyboards are the ones that are writing the code. If they don't fully understand the problem space, it is difficult for them to grasp the big picture.
When the programmer has strong domain knowledge in the area they are programming, it allows them to instinctively understand the edge cases where problems can crop up.
Programming
The first programming that I would have done was working with spreadsheets. It started out with formulas in Microsoft Works spreadsheet. Then we upgraded to Excel and the more powerful formulas that it comes along with. Somewhere along in there, VBA became a part of my Excel development. Then there was a customer that wanted me to add some features to an Access database and that was how I was introduced to Access. Ruby, Elixir, Javascript, and Typescript were studied and learned as I had projects that needed or used them.
Agriculture
All my life I've lived on a farm. We farm both irrigated and dryland crops in Kansas. We currently have some cows. If your programming project involves livestock or grain production, we're going to be able to get right down to the actual problem instead of having to explain all the details about how ag businesses and farming works. Maybe you want to make some printable maps of your fields so you can draw on them as you plan your work, or you want to better communicate with your landowners what is going on, those are good starting points to contact me.
Construction
I worked for ten years on a construction crew doing concrete work. I have experience reading blueprints, laying out foundations, troweling concrete, and digging ditches. If your programming project is going to need good domain knowledge of construction, let me know.