In the SCORM standard, this is defined as

Sum of all of the learner’s session times accumulated in the current learner attempt

In practical applications, it is the total time that a session has been open [this typically means the course is open in a window]. That is different than the interaction time, which is not measured in SCORM.

The SCORM variable is cmi.core.total_time but in SCORM Cloud, it is stored in a field called 'totaltime'. In Bright we follow the SCORM Cloud convention and use the name 'totaltime'.