Tam mak hoong (Lao ຕໍາໝາກຫຸ່ງ, Isan ตำบักหุ่ง or ตำบักฮุ่ง), better known by its Thai name som tum or som tam (ส้มตำ) is a spicy papaya salad originating from Laos and the Isan region of northeastern Thailand. Mak houng (บักฮุ่ง) is the Lao/Isan word for papaya and tam (ตำ) means 'pounded.' The Thai name literally means 'pounded sour.' Tam mak hoong is traditionally eaten with glutinous rice (Thai: ข้าวเหนียว) as a meal, as a spicy vegetable accompaniment, or a snack by itself. The dish is served at room temperature, and often paired with pork rinds and raw vegetables and Ping Gai (Thai gay yang') or roast chicken.

The main ingredient is grated, green papaya. Chili, garlic, lime, fish sauce, brined paddy crabs (ปูเค็ม, bu tem), shrimp paste, and padek are also usually added, while yardlong beans and tomatoes are optional. The ingredients are then pounded in a mortar and pestle to meld the flavours. There are many variations of the dish, some made with carrot or cucumber instead of papaya. As eaten in Laos and Isan, the dish is quite spicy and sour. The Central Thai version tends to be quite mild and sweet in comparison, and often contains crushed peanuts, and less likely to have padaek or bu tem. Dried brine shrimp are also used in this version, commonly referred to as (ส้มตำรามา, som tam rama) whereas the Lao/Isan version is commonly known in Thai as (ส้มตำลาว, som tam Lao).

The dish combines the four main tastes of Lao/Thai cuisine: sour lime, hot chilli, salty fish sauce, and sweetness added by palm sugar.

Numerous other variations exist. Tam mak hoong can also be prepared with other unripe fruits, notably mango, in which case it is known as (Thai: ตำมะม่วง, tam mamuang), cucumber, tam mak teng, or yard long beans, tam mak thua.

The Cambodian equivalent of som tam is bok l'hong. The Khmer version is closer to Som Tam Rama.

Also note that the t in tam (Thai letter ต) is pronounced somewhere between the English letter 't' or 'd', like the Vietnamese letter Đ (See Vietnamese alphabet). As romanisation of Thai is inconsistent, although more commonly seen as som tam, the vowel sound in tam is closer to the English u in gut.