Here’s the simple definition, from Wikipedia:
A chatelaine is a decorative belt hook or clasp worn at the waist with a series of chains suspended from it. Each chain is mounted with useful household appendages such as scissors, thimbles, watches, keys, vinaigrette, and household seals.
However, more important is the implication –
In many countries, the head housekeeper, senior-most woman, “mistress of the chateau,” or “the wife of a castellan” would wear a chatelaine to hold her keys. Thus, it was a status symbol and signified that a particular woman was in charge of running the household and had access to all locked areas.
Why I Looked It Up
From a book about the Vanderbilts:
Gladys was chatelaine of the infinite list of minutiae that go into the running of a grand house…