Unlike the more common variety of olive that is cured in a brine, oil-cured olives are basically, dry-cured olives that get macerated in oil for several months.
The curing removes the bitterness and the resulting olive is shriveled and wrinkly and they sort of resemble small prunes. Because of this curing method, they don't need to be stored in any sort of brine. Depending on the variety of oil-cured olive, the oil may be flavored with various herbs and spices.
The most common oil-cured olive is the black Moroccan. They are meaty and are flavored with cumin, hot chiles, and sometimes citrus. Moroccan cooks typically use them in tagines, although they would also be great on a caramelized onion pizza, tossed in a salad with some frisee, thinly sliced fennel and pears or just for snacking along with some almonds.