A friend recently asked me, "What are capers?" The basic answer is they are the preserved flower buds of a shrub or bush that originated in the Mediterranean area. The buds range in size from about 1/8-inch in diameter to 1/4-inch and are named for the bush, Capparis spinosa L. These days, capers are raised anywhere there's a Mediterranean-type climate including California and parts of Argentina. The culinary answer is bit more complex.
After the buds are picked, they're pickled in either a vinegar brine or simple salt. The pickling process leads to the development of a mild (but distintive) mustard-like flavor - and, in fact, I've used a pinch of dried mustard as a substitute for capers in a sauce, but that's only part of the story. Brined capers also contribute a tart, vinegary slightly-salty flavor, while salted capers add a good dose of salt to a dish - even when rinsed.
And most recipes recommend rinsing capers before using them. But although I always rinse salted capers, I seldom rinse brined capers because I love their acidity. In fact, these days I substitute capers in most recipes calling for chopped dill pickles.
The other contribution capers make to dishes is their texture. They're large enough to feel with your tongue (if you're paying attention) and have the consistency of cooked corn kernels. In sauces, such as with Chicken Piccata, the texture is a huge boost to the overall enjoyment of the dish. I addition, each caper produces a little burst of flavor when you bite into it. These little firecrackers of flavor add tremendously to making a dish fun to eat.