In electrochemistry, polarization is a collective term for certain mechanical side-effects (of an electrochemical process) by which isolating barriers develop at the interface between electrode and electrolyte.
The term 'polarization' derives from the early 19th-century discovery that electrolysis causes the elements in an electrolyte to be attracted towards one or the other pole— i.e. the gasses were polarized towards the electrodes.
In time, as more electrochemical processes were invented, the term polarization evolved to denote any (potentially undesirable) mechanical side-effects that occur at the interface between electrolyte and electrodes.
This in turn can influence reaction rate, and/or accelerate dendrite formation, and/or deform the plates, and/or precipitate thermal runaway.
The mechanical side-effects can be desirable in some electrochemical processes, for example, certain types of electropolishing and electroplating take advantage of the fact that evolved gasses will first accumulate in the depressions of the plate.