A market for a security with a very low bid-ask spread. That is, there is a very small difference between the highest price a buyer is willing to pay and the lowest price that a seller is willing to take. A close market occurs when trading is very active and there are a larger number of market makers working on the same security.
A narrow spread between the bid price and ask price of a security. A close market in a security is facilitated by active trading and multiple market makers.