Here's another excerpt, how another writer characterizes and tries to explain what padek is. This one is from a book called Food from Northern Laos - The Boat Landing Cookbook by Dorothy Culloty, Galangal Press, 2010. Page 41.
"This extremely pungent, opaque fermented fish sauce incorporates chunks of fish. It is eaten raw or cooked in a variety of Lao dishes; it is used extensively in Thailand's Isaan province, home to many Lao. It is also made and used in northern and central Thailand. Padek's odour is so
intense that tam mak hoong can be detected a room away. When the correct amount of padek is added to a Lao dish, however, the sauce magically transforms it, adding a depth not replicable by substituting fish sauce."