The element, used to create a definition lists that matches some terms with their definitions, is missing a required child element.
The following list will cause this issue, as it’s missing a to specify the term the given definition refers to:
A box without hinges, key, or lid, yet golden treasure inside is hid.
Fixing the above example is as easy as including the missing with the term:
Egg
A box without hinges, key, or lid, yet golden treasure inside is hid.
Learn more:
HTML Spec: the dl element
The riddles of Bilbo and Gollum