A market is a platform developed to facilitate the exchange of anything (goods, rights, ownership) between individuals or parties. The side which gives up this ownership is deemed the seller and the one that acquires it is called the buyer. The terms and conditions of a transaction are usually decided by both parties involved either directly or through an intermediary. Whatever the conditions be, markets can be thought of a place where all gather to conduct these activities. Market systems are based on the characteristics of such platforms.
They are mainly based on the nature of these transactions that occur between parties and can be divided into categories based on pricing, regulation, and modes of exchange within a market. In traditional flea markets, prices are set amongst both parties whereas in others, the prices are predetermined in response to the prevailing demand-supply situation. In more others, bidding and voting mechanisms are used to facilitate transactions. On one end there is a Laissez-fare (free markets) structure and on the other lies a market with a high involvement of the government (as proposed by socialism and communism). Whatever the mode of conduct be, these systems are set in place and are mainly determined by sellers, buyers and the government.
Marshall, Alfred. 1961. Principles of Economics, edited with annotations by C. W. Guillebaud, 2 Volumes. London: Macmillan and Co.