Hi, 'SID' in documentation not explained

I'm confused if everyone should be using that exact same string.
In an example where we want to have access to current cookie values, and store new ones along with them in the same group.
Or we can use any string.
Or we should replace that with the Session ID.
Or we should try and find what the current website is using as the Session ID key in the current Cookies.
Or, something else?