This is the 592nd most frequent Greek word.
ασφαλείας
"Ασφαλείας" means "security" or "safety" in English.
In this sentence, 'ασφαλείας' (asefalias) modifies 'κωδικός' (code), providing the context of security or safekeeping.
Ο κωδικός ασφαλείας πρέπει να είναι μυστικός.
The security code must be kept secret.
Here, 'ασφαλείας' (asefalias) qualifies 'σύστημα' (system), indicating its purpose related to safety or protection.
Το σύστημα ασφαλείας του κτιρίου είναι καινούργιο.
The building's security system is new.
In this case, 'ασφαλείας' (asefalias) is part of the term 'ζώνη ασφαλείας' (seatbelt), meaning it's an item ensuring safety.