On: Venus is not Earth’s closest neighbor (2019) [pdf]

[thrdbndndn]

But under what definition of "closet" would it be Venus?

According to CGP Grey's video linked in the comments, not only Mercury has lowest average distance to Earth, it's also spend the most time being the closest planet to Earth, so it already met two definitions I can think of.

[jjk166 → thrdbndndn]

Venus gets closer to Earth than any other planet, which is a perfectly cromulent definition of closest.

[jiri → thrdbndndn]

You can use delta-v, so the closest is the distance rocket use the least fuel/mass. It is a very good measure how easily to get to that destination in space.

[scrollaway → thrdbndndn]

Which orbit is the closest to earths orbit.