The -sT option in Nmap is used to perform a TCP connect scan. This type of scan attempts to complete the TCP three-way handshake with each targeted port. If the handshake is successful, it indicates that the port is open. This scan method is not stealthy because it establishes a full connection and can be easily logged by the target system. It is a reliable method to determine if ports are open on a target, but it can be detected by simple logging mechanisms.