The phenomenon by which the seller of a particular good, service or security desires to maximize the selling price, while the buyer desires to minimize the purchasing price. Generally speaking, the greater the price tension within a particular market, the greater the bid-ask spread.
Price tension tends to decrease liquidity and create price stickiness. If price tension is relatively large within a particular market or exchange, there will be larger bid-ask spreads. Sellers will be asking for more than what the vast majority of buyers are willing to pay, which will drastically reduce the number of exchanges made within the market.
Having little liquidity in a given market exposes the investor to liquidity risk, which can result in drastic changes in the security's underlying value.