What is the function of the special directory(named debian) to the project design?

I am reading a github project:

you see there is a directory(debian) in there, what the function of it?

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I have browsed the directory, there seems have some configuration files:

shadowsocks/debian/config.json

{     "server":"my_server_ip",     "server_port":8388,     "local_address": "127.0.0.1",     "local_port":1080,     "password":"mypassword",     "timeout":300,     "method":"aes-256-cfb",     "fast_open": false,     "workers": 1,     "prefer_ipv6": false } 

what’s the directory here for? and what is the function to the project design?