The phrase "soluble form" refers to a substance that can dissolve in a liquid, typically water. It means that the substance can break down and mix with the liquid to form a solution without any solid particles remaining. Full definition
Thus it is not surprising that the addition of soluble forms of fiber to diets often has been found to improve absorption of minerals. (academic.oup.com)
If you're concerned about heart health, you'll want to get a high percentage of that daily amount of fiber in soluble form. (healthyeating.sfgate.com)
Vitamin E in water soluble form, extracted from vegetable oils. (essentialformulas.com)