What word can be written forwards, backwards or upside down and can always be read correctly from left to right?
forwards, backwards or upside down
I think you mean ambigram
The best palindrome I ever heard about was a newspaper headline (Hearst-?) describing the entrance of the U.S. in the digging of the Panama Canal:
A MAN, A PLAN, A CANAL; PANAMA!
If you rotate something (vertically), the right side ends up on the left.
If you turn something upside down (flip it) the right side remains on the right.
It's the difference between "rotate" and "flip" in many graphics programs.
The following letters remain the same when flipped upside down:
B, C, D, E, H, I, K, O, X. Hence BOXED, BOOB stay the same when flipped, but not rotated.
The following letters remain the same when rotated vertically 180 degrees.
H, I, O, S, X, Z . Hence SOS remains the same when rotated (but not necessarily when flipped)
The following letters remain the same when rotated horizontally 180 degrees:
A, H, I, M, O, T, U, V, W, X, Y . So WOW, YAY, TOOT, (any palindrome with these letters) can be rotated horizontally, but not necessarily flipped or rotated vertically.