This command is used to set the property service
set property service
to enable the GPU overdraw debugging
adb shell setprop key value
adb shell setprop service.adb.tcp.port 5555
It is a command that sets the value of the specified property.
Android system properties are being managed by special property_service database. The asb shell setprop is a setter command used to change/set the values in this database.
Some properties require root access to change them so make sure that you have root access before trying to set the property value.