Bit rate is the speed at which data is transmitted on a communication link, usually measured in bits per second. On serial hardware, it tells you how fast one device can send or receive bytes over the wire. A USB-to-serial adapter that supports a wide range of bit rates can work with many different devices, from slow embedded controllers to faster console links.
In cyber security, bit rate matters because the wrong setting can make traffic unreadable, cause framing errors, or break tools used for debugging and forensics. Attackers may abuse unusual serial settings to hide activity or to make monitoring harder, while defenders use correct bit rate matching to capture console output, recover device logs, and inspect hardware behavior reliably. In practice, reading or setting the bit rate correctly is a basic step when investigating a serial connection.