Souse (the verb) can mean to cover a food in liquid, to plunge a food in liquid, or it can refer to the liquid that is used.
Sousing something can be for the purposes of cooking or pickling.
For cooking, the liquid is often a spiced vinegar solution. For pickling, the liquid is usually brine or a vinegar.
For the meat dish, see Pork Souse.
In English slang, to be “soused” is to be pickled, as in drunk.