Spread is The difference among the bid and the ask price of a security or asset and an options spot established by purchasing one option by selling another option of the same class but of a dissimilar series.

The spread for an asset is influenced by a some of points:

a) Supply or “float” (the total quantity of shares outstanding that are available to trade)
b) Demand on a stock
c) Total trading action of the stock

For a stock option market, the spread would be the difference among the strike price and the market value.