Use iPXE when mentioning the more feature rich iPXE pxe-boot environment.
iPXE is an extended PXE (Preboot eXecution Environment) network boot program (NBP) with support for scripting, HTTP and many other features.
Often, but not always, chained from PXE-BOOT or EFI to get these more advanced features or better performance with it's native NIC drivers.
Also used as a firmware or boot rom. Many emulators, such as Qemu does use iPXE to provide network boot environment.