The phrase "yacht salvage" refers to any operation, voluntary or not, that successfully rescues the boat, passengers or cargo from imminent danger at sea. In addition to employing more than one towing vessel, yacht salvage typically requires the use special equipment such as high capacity pumps.
There is a difference between yacht salvage and towing. Towing normally implies that the circumstances pose no imminent danger to the vessel, and that it can safely drift in the water. Since marine assistance companies offer both towing and salvage services, it is wise to ascertain beforehand whether a company is classifying the situation as a towing or salvage operation, as the difference in costs can vary drastically.