A barrier to entry is the amount of effort, cost, or expertise required to start doing a technical task. In security, it describes how hard it is for someone to develop malware, reverse engineer a device, build an exploit, or, on the defensive side, deploy strong controls and checks. A high barrier to entry limits participation to people with time, money, and specialized skills; a low barrier lets more people experiment, learn, and build.
This matters in cyber security because attackers often benefit when barriers fall. Easy-to-use tools, public code, and inexpensive hardware can make scanning, phishing, or payload creation accessible to less skilled threat actors. Defenders watch the same trend on their side: lowering the barrier to entry for secure practices, such as automation, secure defaults, and clear verification steps, helps more teams do the right thing consistently. In short, barrier to entry shapes who can attack, who can defend, and how widely a technique spreads.