In the context of options trading, OI stands for Open Interest, which refers to the total number of outstanding contracts for a particular option. The OI change is the difference between the current open interest and the open interest at the previous settlement.

In an option chain, the OI change is a metric that is used to track the changes in the open interest for a particular option over time. It can be useful for investors and traders who are looking to understand the supply and demand dynamics of the options market and to identify potential trading opportunities.
For example, if the OI change for a particular call option on the Nifty 50 index is positive, this may indicate that there is increasing demand for the option and that more buyers are entering the market. On the other hand, if the OI change for the same call option is negative, this may indicate that there is decreasing demand for the option and that more sellers are entering the market.

It is important to note that the OI change is just one factor to consider when evaluating options and that it should be used in conjunction with other metrics, such as the bid and ask prices, volume, and implied volatility. Understanding the OI change can be helpful for investors and traders who are looking to make informed decisions about buying and selling options.