What is a gross spread?

The difference between the underwriting price received by the issuing company and the actual price offered to the public.
Investopedia explains Gross Spread as - By charging the public a higher price for an IPO than the price paid to the issuing company, the underwriters are able to make a profit. For example a company might get $15 per share for their IPO, but the underwriters sell the stock to the public at $17--profiting $2 per share.

Gross Spread, Investopedia, Underwriting Price to make profit