A gooseneck is a crucial, usually metal, fitting on a sailboat that secures the boom to the mast, acting as a universal joint. It enables the boom to swivel horizontally (side-to-side) and pivot vertically (up-and-down), allowing the mainsail to be easily controlled, trimmed, or lowered.

Key Features and Functions:
Pivot Point: It allows the boom to move freely as the wind changes or when gybing.

Construction: Typically consists of a vertical pivot (pintle) and a horizontal pivot (eyebolt or toggle) that connects the mast to the forward end of the boom.

Types:
Fixed: Securely fastened at a set height.

Sliding: Rides on a small track on the mast, allowing the crew to adjust the boom's height, often used in conjunction with a downhaul for sail tension.

Origin: The name derives from its curved shape, which resembles the neck of a goose.

The gooseneck is vital for allowing the boom to swing away from the mast while staying securely attached.