Today is Tsiknopempti or the week of Kreatini, during which large amounts of meat are traditionally consumed by Greek Orthodox believers prior to the arrival of Lent, the fasting season leading up to Easter. (The day is also known as BBQ Thursday). It is similar to, but should not be confused with, the French festival of Mardi Gras (or "Fat Tuesday".)
Meat is king, with the emphasis on grilled meats, though the occasional stew pot will be visible. Some hotels and virtually every taverna will put on special menus for Tsiknopempti. By far, the most common item will be some variation of souvlaki - meat on a stick. These will be available everywhere along the streets in the taverna areas and walk carefully to avoid banging into an unexpected grill mostly obscured by smoke, sharing the already narrow streets and walkways. (Souvlaki skewers in the hands of the inexperienced can also be causes of mild injury, so be careful.)
Beyond the standard grilling, each region of Greece also has its own customs and traditions which are celebrated on this day every year.