Weeklys that are part of the Short Term Options Program have a contract duration term of as many as five weeks and are typically listed on Thursdays. The options can expire on any Friday of the month, other than the third-Friday-of-the-month. Also, Short Term Options will not be listed for expiration on a date that an existing contract, such as a Quarterly option, is already set to expire on the same date. In the case of a holiday on the listing date, the listing date is moved back one business day (e.g. from Thursday to Wednesday). In the case of a holiday on the expiration date, the expiration date is moved back one business day (e.g. from Friday to Thursday).
Settlement is the same as regular options on the same underlying, e.g., ETF and equity option series are p.m.-settled, OEX and XEO option series are p.m.-settled, other broad-based index Weeklys options series are a.m.-settled. Note that SPX does not participate in the Short Term Option Series Program and, instead, participates in the "End of Week" Program. They are p.m.-settled on Fridays.
There is currently a limitation on the number of Weeklys classes that can be offered. Specifically, CBOE may select up to thirty currently listed option classes and may also match any options classes selected by other exchanges that employ a similar program.
Note that there are no SPX Short Term Options since SPX Weeklys are part of the End-of-Week Expirations Pilot Program. Short Term Option positions are included with other options in the same class for purposes of margins and position limits. See http://www.cboe.com/products, http://www.cboe.com/Products/OptionsOnETFs.aspx and http://www.cboe.com/Products/EquityOptionSpecs.aspx for links to product specifications for index options, ETFs and equities.
See also CBOE Rules 5.5(d) and 24.9(a)(2)(A).