What is it called when a word is the same both forward and backward?

Words that look the same both forward and backward are called palindromes. Perhaps the most well-known palindromic word is racecar, but there are plenty of others, like wow, mom, radar, solos, reviver, and deified.

Palindrome isn't applied only to single words, though. Phrases and entire sentences can be palindromes (ignoring the punctuation), and many examples already exist and are being created every day. Here's just a small sample:

  • Madam, I'm Adam.
  • Dennis and Edna sinned.
  • Able was I ere I saw Elba.
  • Drab as a fool, aloof as a bard.
  • A man, a plan, a canal: Panama.
  • Yo! Banana boy!