The 'st' in options typically stands for 'style.' The style in this case, generally refers to how the closing of the option contract is handled. European-style options can only be exercised on the expiration date, while American-style options can be exercised any time up until the expiration date. So, if you're trying to figure out when an option expires and you don't see an expiration date listed, just look for the 'st' - it should give you all the information you need.