Sync_gateway config file

hi,
I am very new in couchbase server.
i need to be clear on config.json file , i have created sample config file , i am not able to visualise what is the “Database” in it? what is the significance of it in couchbase server terms?

in config file :
“database”:
{
“db”: {

}
}
what is that db exactly , it is sort of cluster name or database created on server side?