In the context of halophytes a Salt is a compound that is made from minerals (like Magnesium, Potassium, Sodium, Calcium, etc) that is combined with Chlorine.
aka salt = containing Chlorine, in fact the salt that we add to snow to melt it is Calcium Chloride
Soils high in salt usually also have a high pH aka the water is hard aka it has
alot of of dissolved solids.
The main difference between high pH and high salt is that high pH usually have carbonates+mineral (Magnesium, Potassium, Calcium, etc) vs high salt have chlorine+mineral (Magnesium, Potassium, Sodium).
The question now becomes why does these soils have super high pH and or high salt but some other soils dont have it.
It is usually due to evaporation close to or exceeding "rainfall"
"Normally" the dissolved "salt" in the groundwater makes it to the sea and then it gets concentrated via evaporation, and it is that same evaporation process that is increase the salinity of the soil. In some soil near the salty sea water enters the ground water and fouls the freshwater water table.
I am also not too sure that dandelion causes soil compaction or that spinach cause high nitrate soil or that cactus causes desertification or that Tamarix causes high salinity soil more like they are indicator plants.