The Discharge Line carries High Pressure Gas between the Compressor and Condenser
The Suction Line carries Low Pressure Gas from the Evaporator to the Compressor (sometimes through an Accumulator).
The Liquid Line carries High Pressure Liquid from the Condenser to the Evaporator (often through an Expansion Device).
Some assemblies combine two or all three lines together.
A/C Refrigerant Lines
A/C System Repair Toolbox