PXE, or Preboot eXecution Environment, is a technology which allows an enabled network card to access a boot environment via the network. For example one common use is to boot the Windows Preinstallation Environment (WinPE) to install Windows over a network connection without any physical media like an optical disk or USB drive. You can see a good example of that in the video Deploying Windows 7 with Windows Deployment Services.
As qbsinfo mentioned, you can simply disable network boot from the system firmware. Enabling network boot is shown in the video linked, disabling would simply involve changing the setting to disabled rather than enabled.
PXE, or Preboot eXecution Environment, is a technology which allows an enabled network card to access a boot environment via the network. For example one common use is to boot the Windows Preinstallation Environment (WinPE) to install Windows over a network connection without any physical media like an optical disk or USB drive. You can see a good example of that in the video Deploying Windows 7 with Windows Deployment Services.
As qbsinfo mentioned, you can simply disable network boot from the system firmware. Enabling network boot is shown in the video linked, disabling would simply involve changing the setting to disabled rather than enabled.