Phony targets are targets that is not supposed to update or create a file, but is rather a sequence of shell commands to be executed (such as the often seen clean target). Thus, they can thought of as a shell script within the makefile.
In order to specifically tell make that a target is phony, there is the special .PHONY target name:
.PHONY: clean
rm *.o
This .PHONY target name ensures that the rule is run even if a file with the name clean already exists in the current directory.