In an efficient market, prices reflect all available information and perfectly represent the value of products or services. A market price, on the other hand, is simply the price at which a product is sold in any given market. It may not be based on fundamentals but still be influenced by external factors such as supply and demand. Since nobody thinks the same, and people can't (or won't) all access the same information, every product operates in at least somewhat of an inefficient market. There are too many variables that affect price, making it hard to perfectly assess the value of a product.