The number of underlying stocks in a derivatives contract is referred to as the lot size in FnO. For instance, if you wish to buy three put options with a total of 75 underlying stocks each, you must specify quantity as 225 (75*3).
In FnO, lot size refers to the number of underlying stocks in a derivatives contract. Eg: if you want to purchase 3 Put Options each containing 75 underlying stocks, you will have to enter quantity as 225 (75*3)