This category of measurement units is defined by the "weight" type, which is an SI derived quantity. The SI base unit is defined by the "mass" type. Weight and mass are technically different quantities. Mass is an intrinsic property of matter. Weight is a force that results from the action of gravity on matter. For common usage, weight is directly proportional to mass so this distinction is not critical to unit conversions.
The SI base unit for mass is the kilogram. The SI derived unit for weight or force is the newton.
The deprecated unit kilogram-force (kgf) or kilopond (kp) is the force exerted by one kilogram of mass in standard Earth gravity (defined as exactly 9.80665 m/s²). One kilogram-force is equal to exactly 9.80665 newtons.