American and European Options: The terms ‘American’ and ‘European’ refer to the type of underlying asset in an options contract and when it can be executed. American options’ are Options that can be executed at any time on or before their expiration date. ‘European options’ are Options that can only be executed on the expiration date.
A future date on or before which the options contract can be executed. Options contracts have three different durations you can pick from:
Near month (1 month)
Middle Month (2 months)
Far Month (3 months)
Lot size refers to a fixed number of units of the underlying asset that form part of a single F&O contract. The standard lot size is different for each stock and is decided by the exchange on which the stock is traded.
E.g. - Options contracts for Reliance Industries have a lot size of 250 shares per contract. Open Interest:
Open Interest refers to the total number of outstanding positions on a particular options contract across all participants in the market at any given point of time. Open Interest becomes nil past the expiration date for a particular contract.
Example: If trader A buys 100 Nifty options from trader B where, both traders A and B are entering the market for the first time, the open interest would be 100 futures or two contract.
The next day, Trader A sells her contract to Trader C. This does not change the open interest, as a reduction in A’s open position is offset by an increase in C’s open position for this particular asset.
Now, if trader A buys 100 more Nifty Futures from another trader D, the open interest in the Nifty Futures contract would become 200 futures or 4 contracts.