USIM (User Subscriber Identity Module) is the database at user end which can have operator information, their supported bands and lot of other information.
So if i am putting the same logic on your query it would be HSS at operator (Network) side where it has stored all the related info.
Now if i come to your first query:
Home Public Land Mobile Network
Equivalent Home Public Land Mobile Network
As per 3GPP spec ( 24.301) -Page 53 ), The UE shall store a list of equivalent PLMNs for PLMN Selection & cell Selection/Reselection when UE is Switch-Off .
Suppose Your default sim is Vodafone (i.e. your Home PLMN) but when you go to some other places where Vodafone network is not there but operators have consent their business deal and Other network like Idea is there and you are latching on IDEA network, On that time your IDEA will be your EPLMN.