Pound, Mass
The pound is the name of a number of units of mass, all in the range of 300 to 600 grams. Most commonly, it refers to the avoirdupois pound (454 g), divided into 16 avoirdupois ounces. Read more 
In the physical sciences, weight is the downward force exerted on matter as a result of gravity. An object's weight is equal to its mass multiplied by the magnitude of the gravitational field. The word entered Old English sometime around the 9th century, and meant the quantity measured with a balance. The word "weight" is commonly used synonymously with "mass", though the two concepts are technically quite distinct.
Read more
Mechanics