Systemd is responsible to manage Linux system resources. Those resources are known as units, such as services, targets, sockets and so on. It is possible to use systemd to list all of units are made of by the following command:
systemctl list-units
Targets represent the state of Linux has reached during startup. It is also possible to run the above command to filter only for target units:
systemctl list-units --type=target
To get the default target boot has been used for Linux, the following command fit the purpose:
systemctl get-default
To change to another target, the set-default command can help with this task:
sudo systemctl set-default <new-target>