Marouli (Μαρούλι) is lettuce, and in the Greek street and table context it is a component rather than a dish in its own right. The model entry says exactly that: lettuce, sometimes added. It earns an entry here because it is one of the small structural decisions inside wrapped and plated Greek food, the cool crisp layer that goes into a pita or onto a plate, present often enough to be worth describing honestly rather than inflated into something it is not.
The handling is simple and the failures are simpler. The lettuce of choice is the long romaine type, marouli proper, with a firm rib and a leaf that holds shape. It is washed, dried so it is not dripping, and shredded fine across the leaf into ribbons rather than torn into floppy sheets. Fine, dry shred is the whole technique: it gives a wrapped sandwich a layer that stays distinct against warm meat and sauce instead of collapsing into wet pulp. In a pita it goes in as one of the cold elements alongside tomato and onion, positioned so it does not sit directly against the hot filling long enough to wilt before the wrap is eaten. On a plate it is the base or the side that resets the palate between bites of grilled meat. Good marouli is bright, cold, finely cut, and dry. Sloppy marouli is wet from a bad spin, cut in chunks too coarse to fold cleanly, or sat so long it has gone limp and grassy.
How much it matters depends entirely on the format. In a classic gyros or souvlaki pita it is sometimes present and sometimes absent by regional and shop habit, which is exactly why the source flags it as sometimes added rather than standard. As a dressed salad it becomes maroulosalata, lettuce cut fine and dressed with oil, lemon, and dill, which is a dish of its own and deserves its own article rather than being crowded in here. Within the sandwich frame, marouli stays what it is: a deliberate cold layer whose only job is to be crisp, dry, and finely cut.