Pledge is a way to get extra margin for trading by using stocks in your holdings as collateral. To put it simply, pledging is way of taking loans against your stocks. At Groww, You can use the margin received against the pledge only to trade in F&O and Intraday.
There is no interest charged in pledging. However, the user will receive pledge margin after a fixed percentage deduction in pledge value also known as the Haircut.