This is an array of EVENT_CONTEXT:USED user defined labels (normally 16 characters long) that provides the context label strings that may be used in the C3D file typically General, Left, Right, and Invalid.
EVENT_CONTEXT:DESCRIPTIONS
This contains an array of EVENT_CONTEXT:USED descriptions (typically up to 32 characters long) that are associated with the corresponding labels e.g. General events, Left side event, Right side event, Invalid event. This parameter simply provides additional descriptive information for each of the LABELS.