A sauce added to many dishes in SE Asia. Meaning literally "wait fish", it is made by putting fish of any kind in a bucket, putting that bucket out under the SE Asian sun, then retrieving that bucket within a time-frame anywhere between three months to a year. Sometimes, the fish liquid is then boiled in a feeble attempt to remove any parasites.
Also referred to as "pad-ag", in Laotian, it is most commonly added to som tum and a variety of salads and other regional dishes. It, quite objectively, has an indescribably horrible smell--much like a year old fish because it is, in fact, a year old fish.
Person 1: Hey, you want some som tum with pla rah?
Person 2: No, I don't.