This is an array of user defined strings – typically sized as (EVENT:USED,16) – that is used to record a “context” for each event e.g. Left, Right, General etc.  The string used for each event is chosen from a list stored in the EVENT_CONTEXT:LABELS parameter.  This enables a “side” to be assigned to bipedal events where the observer is interested in left versus right side data or could just as easily describe “up” versus “down” events too.