A 'Killer App' (short for 'killer application') is a software program or feature so desirable and innovative that it proves the core value of a technology, driving mass adoption. In cybersecurity, a killer app could be a groundbreaking security tool or platform that compels organizations or individuals to adopt new security standards or technologies. Historical examples outside cybersecurity include spreadsheets for personal computers or email for the internet. In the cybersecurity context, a killer app might be an advanced threat detection system or an intuitive password manager that significantly improves security posture, making the underlying technology indispensable.