This is a chassis-wide running total of every CFM frame the device has transmitted across all maintenance associations and message types, exactly as its description states. Because it aggregates all CFM traffic types (CCM, loopback, linktrace, delay/loss measurement) rather than breaking them out, it is the single number an admin checks first to confirm the CFM engine is generating traffic at all before drilling into the more specific per-message-type Tx counters. If this counter is stuck at zero on a device with several configured MEPs, that alone tells the admin CFM is not running, with no need to check the detailed counters yet.