(The sh in this name is pronounced like one between the s in 'so' and sh in 'she' and ch is pronounced like ch in 'such' .)
Shachi is wife of Indra, the ruler of the three worlds. Being Indra's wife, she is referred to as Indraani(=Indra's wife). She is the daughter of a demon named Puloma and hence was referred to as Poulomi (=Puloma's daughter).
She is reckoned one among the great pathivratha(chaste and faithful wife)s.