^SSADMIN is a TrakCare utility so you will need to look in the TrakCare documentation on that (and/or add the TrakCare tag to this question - not sure if that will send out new notifications to people who follow that Tag).  The Production page from the SMP is for the InterSystems IRIS Interoperability Productions for which I linked docs above.  I am guessing the "Interfacing" is a specific TrakCare feature which uses Productions and other pieces of InterSystems IRIS Interoperability beneath the covers. 

@Phillip Wu - you will need to be a little more specific.  There are a number of 'Gateways' in InterSystems products (e.g. Web Gateway, SQL Gateway, etc), but I don't know of any of them that are specifically an interoperability component.  You could have an interface which uses a gateway to get data, but again the specifics are really important here :)   Also, if you are using a production that someone else created, they could call something a "Gateway" which is their term and not necessarily indicative of something specific to an InterSystems product.