Is MeterStop value the total charged during 1 session or the total since the meter has been installed?

[RobbeVW]

The StopTransaction request holds a parameter called MeterStop.

In the documentation, it mentions the following:

  /**
   * This contains the meter value in Wh for the connector at end of the transaction.
   *
   * @return meter value in Wh.
   */
  public Integer getMeterStop() {
    return meterStop;
  }

Does this mean this parameter returns the meter value for the total Wh charged during that session or transaction. Or does this mean the total that has been charged since the meter was ever installed? Both OCPP documentations and this one are open for interpretation.