LSL is defined here as the distance between the sea surface and the ocean bottom. It is this quantity that is directly related to the potential impact of global and regional changes in climate and sea level in a given area. At any location, LSL is the result of a number of forcing processes acting on a wide range of spatial and temporal scales.
LSL is an absolute quantity in the sense that it does not depend on the reference frame it is measured in. Sea surface height, on the other hand is in that sense a relative quantity.
It is worthwhile to mention here that Global Sea Level (GSL) change is the spatial integral of LSL changes over the complete ocean area and directly related to the change in the global volume of the ocean. Volume changes are the sum of steric changes resulting from temperature and salinity changes and actual changes in the ocean water mass through exchanges with other reservoirs in the global water cycle.