Learn English – What’s the difference between “generally” and “usually”

"Commodity" has a special meaning as a raw product that is generally the same from one batch or producer to the next. While you can can buy a pound of a particular brand of pinto beans from the grocery store, pinto beans are traded in the stock market in much larger quantities based on a "commodities" price.

You might hear the phrase "a rare commodity". That kind of twists the meaning to suggest that the thing is special. Patience is a rare (valuable) commodity in teachers.

"Products" and "goods" (in that sense) are fairly interchangeable words. Product has a bit more sense of specificity. Peanut butter is among the goods typically found in grocery stores, Skippy peanut butter is one of the products you might find on the shelf. You're more likely to see "goods" (plural) than a "good".

Piss would be considered more vulgar, pee would be considered more mild and informal.

It's common to ask a young child, "Do you need to go pee?" I wouldn't ask a young child, "Do you need to take a piss?"

The words also have differences in how they are used, as those questions show. You can go pee, and you can take a piss. (Other variants may apply, with differences in how standard they might be. I wouldn't say that take a pee or go piss are unacceptable, but they don't seem as common.)

Piss can also be used a slang verb. To get pissed is to get very angry. (For example: Joe was pissed about his traffic ticket.)