Currently, the term pound generally means the international avoirdupois pound. Prior to 1959 in the United States and 1963 in the United Kingdom it referred to the then-current magnitudes of the United States customary avoirdupois and British Imperial pounds, which were superseded in those respective years by the international avoirdupois pound. (Troy, apothecaries, and other pounds had been in use in both countries, but had been declared obsolete.)
It should be noted that officially the pound is defined in terms of the kilogram, which by implication makes it a unit of mass. However, the term is normally used in the United States, and has been used as well in the countries employing the British Imperial system of units, to denote both a unit of mass and a unit of force, the common system in use in the US and formerly in the other countries is by implicaton the unit force-mass FPS system.