84. What is the name of the opening in a bilge margin bracket that reduces the weight of the bracket without materially reducing its strength?

Lightening holes are openings cut into structural members to reduce weight without significantly compromising strength, as described in the question. This contrasts with drain holes (for drainage), air holes (for ventilation), and manholes (for access), which serve different purposes. Lightening holes are a standard feature in ship construction, including bilge margin brackets, to minimize weight while maintaining structural integrity.