The terms Master/Slave and Primary/Secondary can usually be used interchangeably. I believe the terms Master/Slave were introduced when Bind 8 came out.
Technically, you can setup your DNS configuration with multiple Master DNS servers or with one Master DNS server and multiple Slave servers or any variation of the two. Maintaining multiple Master DNS servers can be a chore and I wouldn't recommend it unless you have a high number of zones to serve where one Master DNS server could not keep up with constantly updating slave servers.
The 0.168.192.in-addr.arpa entry would be used for reverse DNS entries on IPs in the range 192.168.0.x. Notice the backwards placement of the IP.