This reports how many modules on this phase are deliberately powered off by an operator, manually-off, as opposed to failed, a state that's operationally very different from a fault even though both reduce the phase's active module count. For correctly interpreting a drop in tsiPhaseNbModOK, if that drop is fully explained by an increase in this manually-off count, it's an expected consequence of planned maintenance rather than an unplanned fault, and shouldn't trigger the same urgency as an increase in tsiPhaseNbModKO. An admin reviewing an alert about reduced active modules on a phase would check this count first to rule out a technician simply having taken a module offline intentionally for servicing.