Markets

This is the consensual exchange of goods/services between parties. It uses the price system to ascribe a subjective number value that represents the cost to attain those goods/services. This price being subjective, mellows out according to what market participants are willing to pay for said goods/services at a particular time which is how we arrive at the market price.

A market is just the aggregate of individual Trades — positive sum for the same reason any single trade is: both sides value what they’re getting more than what they’re giving up.