Salmuera is Spanish for brine, or put even more simply salt water.
You’ll see it called for sometimes in Latin American recipes, especially Argentine ones.
Because it’s just salt water, it’s very easy to make.
Whisk 2 teaspoons of fine salt or 1 tablespoon of a coarser salt, such as Maldon, Kosher or a coarse sea salt, into 1/2 cup (4 oz / 125 ml) warm water. Set aside for it to cool and dissolve; stirring occasionally will speed the process. Coarser salt might need an additional whisk after a while to encourage it to dissolve more quickly.