In simpler terms, Pledging is basically taking loan from your broker against the securities that you own.
You can read more on this here : What is pledging, and how does it work?
You can also learn more about Pledging by checking out this TradingQ&A thread:
Related to Pledging:
Exchanges stipulate that for F&O positions, 50% of the margin needs to compulsorily come in cash or cash equivalent collateral, and the remaining 50% can be in terms of non-cash collateral margin. If sufficient cash margin is not maintained and the shortfall is funded by the non-cash collateral, there will be a delayed payment charge of 0.035% per day or 12.5% per annum on the shortfall in the cash margin requirement.