Should be considered a ligament)Master & Slave; b)Secondary & primary separately
a) Master — it can be created and managed DNS records, and Slave already pulls them master these concepts from the point of view of the server settings themselves
b) Primary and Secondary should be considered from the point of view determine the order for domain registration, a NS primary, some secondary, some tertiary, etc. In some areas the order is not relevant and Primary and Secondary blurred.
At the same time, Secondary (as well as Primary) can be the domain Master (i.e., changes are made directly on it) and Slave (to pull information from the master).