fish sauce
There is barely a savory Southeast Asian dish that does not have fish sauce. It's an interesting ingredient made from fermenting fish and sea salt for several months. The mixture is then drained, and the liquid left behind is your fish sauce. It is definitely salty but adds this rich "umami" to your foods.
Now, you might not know this, but a similar condiment was popular in the Ancient Roman Empire: Garum. Yes, garum was made in a similar manner as fish sauce, and Roman soldiers used it on everything from meat to porridge.
Some people think that it is a bit smelly, but when combined with other ingredients the fishiness dissipates.
Fish sauce has a pale amber color, and it is almost transparent. If you don't think you're ready for this exotic ingredient, there are multiple substitutes out there that you can make at home. There are even vegan substitutes.
In Thailand they are called nam pla, and nuoc nam in Vietnam.