Parameters in config/

I see there are uncommon key:value in config/ in frappe and erpnext.
Can anyone please explain what they each mean?

"system_manager": 1,
"condition": getattr(frappe.local.conf, 'developer_mode', 0)
'standard': 1,
"reverse": 1,

and then there is one for restaurant that has different keys. Why is it different?

"module_name": "Restaurant",
"_doctype": "Restaurant",
"link": "List/Restaurant",

also this one in config/

"onboard": 1,

Thank you.