Imbalance of Orders

A situation when too many orders of a particular type - either buy, sell or limit - for listed securities and not enough of the other, matching orders are received by an exchange. Also referred to as "order imbalance".

Investopedia Says:
Shares experiencing an imbalance of orders may be temporarily halted if trading has already commenced for the day. If it occurs prior to market open, trading may be delayed. Better-than-expected earnings or other unexpected good news can result in a surge in buy orders in relation to sell orders. Likewise, unexpected negative news can bring a large sell-off.

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Too many orders of one kind-to buy or to sell-without matching orders of the opposite kind. An imbalance usually follows a dramatic event such as a takeover, the death of a key executive, or a government ruling that will significantly affect the company's business. If it occurs before the stock exchange opens, trading in the stock is delayed. If it occurs during the trading day, the specialist suspends trading until enough matching orders can be found to make for an orderly market.