Short answer
Subclass 102 is a permanent visa for a child outside Australia who has been adopted, or is being adopted, by an eligible Australian sponsor.
The subclass 102 Adoption visa is for a child outside Australia who has been adopted, or is in the process of being adopted, by an Australian citizen, Australian permanent visa holder or eligible New Zealand citizen.
The visa supports family unity by allowing an eligible sponsor to bring their adopted or prospective adoptive child to Australia permanently.