A word or phrase that reads the same backward as it does forward is called a palindrome. The letters are typically read without considering spaces, punctuation, or capitalization, as in “madam,” “racecar,” and “A man, a plan, a canal, Panama.” Palindromes can also be numbers, such as 1221, or sequences of symbols.
The word palindrome was introduced in English by writer Henry Peacham in 1638, but the idea is much older. Ancient Greek and Latin examples include the Sator Square, a word square dating to the first centuries CE. Palindromes also appear in biology: a DNA sequence can be palindromic when its reverse matches its complementary sequence.
A common mix-up is confusing a palindrome with an anagram. An anagram rearranges letters to form another word or phrase, while a palindrome preserves the same sequence when reversed. Not every phrase that sounds repetitive is a palindrome; the letters or chosen units must genuinely match in reverse order.