Power Line Communication (PLC) transfers data over the same cable that is used for power transmission. PLC is particularly useful in scenarios where you want to eliminate the number of cables in a system. Having one cable that runs both power and data makes a system more compact and less complicated to put together.
You already know Power Line Communication from your everyday life. Take for example the charging cable for your phone. Plug it into a computer and it can both charge your phone while also transferring data.