An option class is a group of all the same type of option on a single underlying asset. Options can either be call options, which grant the owner the right, but not the obligation, to buy a certain asset at a pre-determined price within a given timeframe, or put options, which grant the owner the right, but not the obligation, to sell a certain asset at a pre-determined price within a given timeframe.

An option class consists of all call or put options for a particular underlying asset. An option chain, on the other hand, includes both call and put options listed on some security. The number of options in an option class will vary depending on the level of market liquidity of the underlying asset, as well as the amount of trading that takes place in the underlying asset’s options market.

Options classes become even more granular when they are divided into options series. An options series consists of all calls or puts on some underlying asset with the same expiration date. All options in the same option series have the same size, type, and expiration date. For example, if a trader purchased two call options with the same strike price and expiration date, those two options would make up one series - even if the underlying asset changed in the meantime.

It is important for traders to understand option classes and option series in order to make informed decisions when selecting options to trade. Options classes provide an easy way to group different options on a single asset. Option series, as a subset of an option class, provide an even more detailed way of breaking down options into specific expiration dates, which can help traders make decisions regarding the potential timing of their trades. By using both options classes and option series, traders can quickly assess the market conditions of both the underlying asset and its options.