The following are terms used within the industry which you may find helpful:
The resin bed, which collects the magnesium and calcium salts which give hard water needs to be regenerated on a regular basis to continue functioning. This is achieved by passing a solution of brine through it and the process is known as regeneration.
A solution of water and salt.
The regeneration process creates an ion exchange when magnesium and calcium salts are exchanged for sodium.
All ion exchange water softeners contain resin beads which, after regeneration, hold sodium ions ready to exchange with the magnesium and calcium ions dissolved in hard water.