OI buildups are the classification of market sentiment based on Price & OI change of the future contracts for one trading session. It has 4 types -
Long buildup - If price of the contract increases with the increase in OI, it means new long positions have been created for the contract that has led to increase in price of the contract
Long Unwinding - If price of the contract decreases with the decrease in OI, it means that existing long positions have been closed that has led to the decrease in price of the contract.
Short buildup - If price of the contract decreases with increase in OI, it means that short positions have been created for the contract that has led to the decrease in price of the contract.
Short Covering - If price of the contract increases with the decrease in OI, it means that existing short positions have been closed that has lead to the increase in price of the contract.