Pickling is the process of preserving food using a brine (saltwater) solution. The salt in pickling acts on the food by drawing out the water from its cells and kills any bad bacteria that may spoil the food. The process that occurs inside the brine is called fermentation, but the act of making brine and placing food into the saltwater solution is called pickling.
Pickling also usually requires added heat through a canning process, whereas fermented goods can sit out on your shelf and don't require heat. Fermented foods thrive in anaerobic conditions and make use of naturally occurring "good" bacteria submerged under the saltwater. Fermented foods have a bit of a tangy flavor, while pickled goods taste salty or vinegary all the way through.
Pickles are generally associated with the traditional cucumber in brine, but you can pickle all kinds of things, from fruit and vegetables to meat, fish, and eggs. In India, some of the most popular pickles are made from mango and lime. In Europe, you'll find pickled herring, olives, and beets. From Asia to Europe, the world of pickling is vast and varied.
Pickles are often added to a meal to help aid with digestion, giving your body that extra bit of Lactobacillus acidophilus it needs to restore some healthy gut and intestinal flora.
The role of salt in fermentation is to help draw out water from foods and make a salty living environment so bad bacteria have little chance of survival. A brine is created in fermented recipes to preserve fruits and vegetables or other food products.
Making brine can be a bit of an experiment, and the salt measurements sometimes depend on your personal preference. A little salt goes a long way! Some brine even contains a bit of sugar to balance out the salty flavor.