In
/etc/udev/rules.d/
everyone may define their own USB device naming rules.
Here it is possible to create device names such as but not limited to
/dev/razberry
/dev/optoma
/dev/jeelink
/dev/cul868
etc.
instead of cryptic ones like
/dev/AMA0
/dev/ACM0
/dev/USB0
/dev/USB1
The later is the use case for this rules:
Assumed you have 2 USB->RS232 devices connected to your Raspberry Pi, both using the same adapter chip like the FTDI, they will be numbered /dev/USB0 and /dev/USB1. Now this is dangerous. If you replug them in an arbitray order into the usb sockets, the numbers may change. To prevent this the udev rules were invented.
You may even fix permissions (!), owner and group in rules, and they are automatically applied every time you plug in your device, no manual interaction needed and it will survive a reboot.
See for example: