An extremely popular seasoning sauce in Thailand. It is composed of fermented soy beans, salt, sugar and flavour enhancer, apparently not MSG, but a disodium guanylate. It is sold in different bottles according to the protein content, which can be up to 16%, making it good stuff for vegetarians.
This style of sauce has been made for centuries, but the Golden Mountain name was used after the eponymous company manufacturing the sauce was founded in 1954, by a Mr. Chai Saekow. It has since become a generic name for the seasoning.
It can be used in much the same manner as soy sauce, but has a much deeper, somewhat saltier taste even though they look practically identical. It is particularly effective in stir-fries pungent with chilli, such as the one under Thai basil. Everytime I cook with this sauce, it elicits the response, "what did you put in this? It tastes great."
There is a similar product sold under the name of Maggi seasoning sauce, but I don't recommend it because it is twice the price as Golden Mountain and made in Switzerland, hardly the centre of the stir fry world. In addition Maggi is part of the naughty Nestle supercompany. Try and buy the original, it is readily available at most Asian grocery stores.