I understand that it’s a tradition. But I don’t understand exactly what it is

In: Other

It is a philosophy (or sometimes pseudo-religion) that has the basic premise of god (or the divine) being a part of physical reality and vice-versa.
It was considered to be an occult (hidden) science as it contradicted many Christian concepts, and in its heyday it was wise to hide that from regular people and the church to avoid getting jailed or worse.

You can think of it as a philosophy that sits kind of in between true religion and pure science/logic. It accepts scientific discovery and inventions but allocates their existence and logic to a divine entity.

Its rise in popularity in Europe happened when science was starting to play a major role in explaining things, but people were still too religious to completely forego the concept of someone/something “organizing” it all.

Alchemy was a big part of it, which later influenced the development of chemistry and other sciences.