What Is the Bid-Ask Spread?
At any moment, a stock has two prices: the highest price a buyer will pay (the bid) and the lowest price a seller will accept (the ask or offer). The gap between them is the bid-ask spread.
What the spread tells you
The spread is a direct read on liquidity. A heavily traded large cap might have a spread of a few paise — tight, because there are many buyers and sellers. A thinly traded small cap can have a wide spread, meaning you lose more to the gap every time you trade.
The hidden cost
The spread is a real cost. If you buy at the ask and immediately sell at the bid, you lose the spread — before any brokerage. On illiquid stocks this can be significant, which is why liquidity matters as much as the headline price.
Liquidity in the data
While end-of-day data shows one closing price (not live bid/ask), liquidity signals like trading volume and delivery percentage are available and feed the screener. Low volume usually means a wider spread.