Brining

In cooking, brining is a process similar to marination in which meat is soaked in a salt solution (the brine) before cooking.

Brining makes cooked meat moister by hydrating the cells of its muscle tissue before cooking, via the process of osmosis, and by allowing the cells to hold on to the water while they are cooked, via the process of denaturation. The brine surrounding the cells has a higher concentration of salt than the fluid within the cells, but the cell fluid has a higher concentration of other solutes. 

This leads salt ions to enter the cell via diffusion. The increased salinity of the cell fluid causes the cell to absorb water from the brine via osmosis. The salt introduced into the cell also denatures its proteins. The proteins coagulate, forming a matrix which traps water molecules and holds them during cooking. This prevents the meat from drying out, or dehydrating.

In many foods the additional salt is also desirable as a preservative. Note that kosher meats are salted during the process of koshering so they should not be brined.

Some cheeses are periodically washed in a saltwater brine during their ripening. Not only does the brine carry flavors into the cheese (it might be seasoned with spices or wine), but the salty environment may nurture the growth of the Brevibacterium linens bacteria, which can impart a very pronounced odor (Limburger) and interesting flavor. The same bacteria can also have some impact on cheeses that are simply ripened in humid conditions, like Camembert. Large populations of these "smear bacteria" show up as a sticky orange-red layer on some brine-washed cheeses