Thick paste made from olives, usually black ones; Kalamata olives make a great olive paste. Olive paste is a nice addition to a vinaigrette, or try spreading it on crackers for quick crudites.
You can make your own olive paste, perhaps using sneff's recipe for tapenade, which adds capers, anchovies, Dijon mustard, garlic, cornichons, olive oil, brandy, and pepper to pitted olives. (A tapenade is generally less finely ground than an olive paste; put yours in the food processor for that real paste consistency.)
Sneff just says to discard the pits, which might sound daunting, but pitting an olive is easier than you might think, especially if it's a black or dark-coloured one. (Green ones, being less ripe, cling much harder to their pits.) Put the olive on a cutting board and press down firmly with a large knife till you feel the olive break open. Then just pull the pieces of the olive away from the pit. Word of warning: it takes a lot of olives to make a significant portion of olive paste, and if you're using black ones they make a gucky mess under your nails. But these are the sacrifices we make in pursuit of culinary excellence, aren't they?
Or you can buy olive paste at the deli; just make sure you get a good one.