Unbalanced has a few uses. Physically, it means not steady — something unbalanced might tip over easily, like a table with one short leg. For ideas, reports, or diets, unbalanced means unfair or unequal — it gives too much weight to one side and not enough to another, like 'an unbalanced diet' (too much of one kind of food) or 'an unbalanced report' (only telling one side of a story). There's also an older use where people called a person 'unbalanced' to mean their mind seemed disturbed — this use is now old-fashioned and can sound harsh, so it's better avoided when talking about real people today.