In cybersecurity, 'rules' are predefined instructions or criteria that guide systems in detecting, allowing, or blocking certain activities. These rules can specify what network traffic is permitted, which files are considered safe, or how to respond to specific threats. Often used in firewalls, intrusion detection systems, and antivirus software, rules help automate security decisions. While effective for handling predictable scenarios, they may struggle to adapt to new or evolving threats without frequent updates.