1.
beef (or pork) and egg rice bowl
A rice bowl dish topped with sliced beef or pork simmered with onions in a sweet soy-based broth, then bound with beaten egg. Named in contrast to 親子丼, which uses chicken and egg.
The name is a playful contrast with 親子丼 (parent-and-child bowl). In 親子丼, the chicken (親, parent) and egg (子, child) are related, so they are "parent and child." In 他人丼, the meat (beef or pork) and egg are from different animals, so they are "他人" (strangers/unrelated people).
Common collocations
Regional note
他人丼 is more commonly known in the Kansai region. In Kanto, it is sometimes called 開化丼 (civilization bowl), a name dating back to the Meiji era when eating beef became popular.