Difference between DNS stub zone and secondary zone

What is a DNS STUB zone?

A stub zone is a copy of a zone that contains only those resource records
necessary to identify the authoritative Domain Name System (DNS) servers for
that zone. A stub zone is used to resolve names between separate DNS namespaces.
This type of resolution may be necessary when a corporate merger requires that
the DNS servers for two separate DNS namespaces resolve names for clients in
both namespaces.
The master servers for a stub zone are one or more DNS servers authoritative for
the child zone, usually the DNS server hosting the primary zone for the
delegated domain name.

What does a DNS stub zone consists of?

A stub zone consists of:
 The start of authority   (SOA) resource record, name server (NS) resource
records, and the glue A   resource records for the delegated zone.

The IP address of one or   more master servers that can be used to update the
stub zone.

Standard DNS Secondary Zone

A secondary name server gets the data for its zones from another name server
(either a primary name server or another secondary name server) for that zone
across the network. The data in a Secondary zone is Read only, and updated
information must come from additional zone transfers. The process of obtaining
this zone information (i.e., the database file) across the network is referred
to as a zone transfer. .
Secondary servers can provide a means to offload DNS query traffic in areas of
the network where a zone is heavily queried and used. Additionally, if a primary
server is down, a secondary server can provide some name resolution in the zone
until the primary server is available.