IRELAND NORTHERN 10 Pounds 1977 Specimen Unc Rare

What does Specimen mean:

Central banks transmit so-called specimen banknotes (or specimen) to other banks before issuing new banknotes. To avoid its use as a legal value coin, the banknote is perforated or punched, it is assigned the serial number 9999999999 (all nine) or 0000000000 (all zeros) or is overwritten with the word Specimen or Erased in several languages. In Italian it is also called facsimile.

These banknotes are highly sought after by collectors.