If there is a significant supply or demand imbalance and lower liquidity, the bid-ask spread will expand substantially. (Investopedia)

For example, the market maker would quote a bid-ask spread for the stock as $20.40/$20.45, where $20.40 represents the price that the market maker would buy the stock, and $20.45 is the price that the market maker would sell the stock. (the balance)

Many traders and analysts scrutinize patterns in bid-ask spreads to understand what prices trigger demand for both sellers and buyers. Other traders and analysts feel that the bid-ask spread itself has little predictive value. (InvestigatingAnswers)