A kilogram is a measure of mass. A pound is a measure of force.
Mass is the amount of matter you have, but force is a measure of push or pull one object has on another, and,according to Isaaac Newton, is measured by the expression F=ma or "Force = Mass times acceleration". Weight is a force that needs to fit that expression.
To make it worse, some dope somewhere conceived of the "kilogram-force" and somehow made it so it does not fit into F=ma.