Pound is a unit of mass in U.S customary, imperial and other different measurement systems including the historical ones (Romans called it "libra" and that's why it's abbreviated as "lb" and "lbs" today). After the metric system is accepted in many countries, it's replaced with "kilogram" but it's still one of the most common weight units in u.s, u.k., canada and a few other countries.
The avoirdupois lbs is defined to be exactly 0.45359237 kilograms and it is commonly used as a weight unit today. Troy lbs is rarely used since troy weight system is used for precious metals and jewellery weight measurement and ounce is a better fit to measure small amounts. The abbreviations are "lb" and "lbs".
Ounce is used as a unit of mass in imperial and U.S. customary measurement systems. It is also used as a volume unit but in this case, fluid ounce is referred. The abbreviation is "oz".