The correct answer is (C) delicate ornamental work; work of fine gold or silver, or copper wire formed into delicate tracery; lacy ornamental work of fine gold, silver, or copper wire. Any delicate or fragile openwork of fine metal.

Filigree comes from French filigrane, Italian filigrana, Latin filum (thread), granum (grain)

Examples of use:

• He finds it important to use a good source of light when working on filigree.
• She kept her mother's photograph in a picture frame of silver filigree.