/Users/USERNAME/Library/Application Support/
Edit:
This answer has drawn a lot of upvotes despite its minimalistic nature. Therefore, I want to point out the things mentioned in the comments here to make them more visible:
- There are several other folders being used for application data / configuration, as mentioned in this answer.
- If writing an application, don’t hardcode that path. Instead, use macOS’ API to retrieve it. This question has several answers for both ObjectiveC and Swift.