two-way mirror is one in a pair of mirrors that are magically connected. This allows people to communicate with each other between locations.There are two or three sets of mirrors in use in the AoD universe.
Alice's Mirrors Edit Alice Longbottom gave her son Neville Longbottom an enchanted mirror when she visited him in the Slytherin Academy the second time. They used them several times, including to get information from Neville about Pansy Parkinson after her capture.
When Neville entered the service of
Evan Rosier, he gave the mirror to Ginny Weasley for safekeeping. She used the mirror once to contact Alice and let her know what had happened to her son.
Fred and George Weasley entered the Outsider's House, they borrowed Alice's half of the mirror to contact their sister.
Terrence's Mirrors Edit
Sirius and James' Mirrors Edit
James Potter's and Sirius Black's mirrors have not been used in game, but they are presumably still in their possession.