What is Shipped
The developer's work has reached real users: published releases, live demos, deployed products, or packages people install.
In plain terms
Shipping is the act of getting software all the way to the people who use it: a published release, a live demo, a deployed product, a package other people install. Plenty of capable developers write code that stays private, and carrying work over the finish line is a distinct, hireable habit.
What it tells you about a developer
A developer with a shipping record finishes things under real-world constraints, and has felt the consequences of their own decisions in production. That experience transfers directly to any product team.