Linux bridge: what does master mean in the "ip link set"?

In the following diagram, each color stands for a network namespace, which is connected by a Linux bridge v-net-0. - veth-red and veth-red-br are a pair of veth. - veth-blue and veth-blue-br are a pair of veth. - v-net-0 is a linux bridge. what does "master" mean in this command?

ip link set veth-blue-br master v-net-0

I have checked the man page of ip link set, but still don't understand the meaning of flag master.