The $ORIGIN command is a way of changing the origin in a data file. The line starts in column 1, and is followed by a domain name. It resets the current origin for relative domain names (for example, not fully qualified names) to the stated name. This is useful for putting more than one domain in a data file.
You cannot use $ORIGIN() for putting more than one zone in a data file.
Use of $ORIGIN commands in a data file is optional. If there is no $ORIGIN() statement the default origin for DNS data files is the domain named in the second field of the master or slave line of the named.conf file.