Air Conditioning Drain Pump
Cold surfaces accumulate water from the air.  For an air conditioner, the indoor unit is the cold one that needs a drain line running somewhere to get rid of accumulated condensate (otherwise the indoor unit will drip water).  In the case of a heat pump in heating mode, the outdoor unit will accumulate water, but there is no need to pipe that water anywhere else.

Because mini-splits are often installed away from any convenient drains, pumps are frequently used to send the condensate where needed.  Depending on the pump used, the condensate can be moved long distances.

With proper installation the condensate can be disposed of into the sewer or often directly outside.  Where condensate is disposed and how the piping must be installed is determined by manufacturer specifications and local building codes.  Your suppliers should be familiar with the requirements.