The pound or pound-mass (abbreviation: lb, lbm, or sometimes in the United States: #) is a unit of mass used in the imperial, United States customary and other systems of measurement.

A number of different definitions have been used, the most common today being the international avoirdupois pound of exactly 0.45359237 kilogram.

The word pound comes from the Latin word pendere, meaning "to weigh".

The Latin word libra means "scales, balances" and it also describes a Roman unit similar to the pound-force. This is the origin of the abbreviation "lb" for the pound.

oh...from wiki: In the past, they were more commonly referred to as "dog pounds", a term which had its origins in the pounds of agricultural communities, where stray cattle would be penned up until claimed by their owners.

My guess WOULD have been short for "impound" but Wiki proved me wrong. Personally, I'd always wondered, too. Nowadays, the official name is usually Animal Control.