A gyro refers to a dish made from huge cylindrical block of lamb, chicken or pork meat, sometimes ground and sometimes layered. It is cooked vertically, in rotisserie style, and shaved to put on a pita with various toppings. This meat is heavily spiced and seasoned, with a herbal blend that enhances the mild flavor of the slow cooked meat.
Marjoram is an herb closely related to mint, but with a savory flavor similar to oregano. In many Greek-style dishes, oregano is often substituted in place of marjoram because it's more commonly found in supermarkets. This should be added in equal proportion to the other spices and preferably ground so that it can be rubbed on the meat.
Paprika usually comes in two common varieties: sweet and hot, with smoked paprika becoming more common these days. Paprika is made from dried bell peppers, crushed into a fine powder, and is very common in Hungarian and Turkish dishes. Turkey is where the doner kebab originated, which is the culinary ancestor of the gyro.
Rosemary is a woody herb that pairs well with the mild flavor of lamb. The taste is somewhat bitter but the smell is very aromatic, which is intensified when the herb is dried. Rosemary should be ground in a food processor or with a mortar and pestle before being added to a spice rub.
White Wine Vinegar
After rubbing with spices -- including salt and pepper -- a gyro loaf should be brined in white wine vinegar for 24 hours before it is put on the rotisserie. This not only flavors the meat, but saturates it so that it is much less likely to dry out as it's cooking.