In plain terms. The NFS is NASA's supplement to the FAR, adding NASA-specific acquisition rules.
Who it applies to. Contractors providing space, aeronautics, research, and IT to NASA.
What it requires. Comply with the FAR, then NASA additions in the NFS. NASA work often involves covered technical information and export-controlled data, so expect information-security and data-handling requirements accordingly.
Why it matters. Technical and export-controlled data is common on NASA contracts, where mishandling can carry both contractual and export-control consequences.
Citation. NFS, the NASA FAR Supplement supplement to the Federal Acquisition Regulation (FAR), codified in the FAR System at Title 48 of the C.F.R.