Peth is Xens name for "Physical Ethernet". With Xen distributions, custom naming rules were set up due to the large number of physical and virtual devices on a system.
However, most linux flavors these days using systemd are going to have rules defined that ensure the interface gets its same name across reboots. This is due to the growing number of systems with multiple interfaces - and is designed to protect against NIC1 being named "Eth0", but then getting named "Eth1" after a reboot. You can see the rules for this in /usr/lib/udev/rules.d/ - the rules that apply to the network interfaces are in 80-net-name-slot.rules.
You can even create a custom version of this so your devices all get named after Peanuts characters, if you'd like. Thats part of Systemd and udev rules.