Nano-SIM

(4FF SIM)
4FF stands for 4th Form Factor.
A SIM card that is simply physically smaller than a traditional (2FF) SIM card or Micro-SIM (3FF) card.
See: SIM
The electric contacts and circuitry of a Nano-SIM are identical to that of a larger SIM card; the plastic part is simply smaller. A nano-SIM can be used in a larger SIM card slot with an adapter.
See: Micro-SIM