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

Palindrome

Each restriction endonuclease functions by ‘inspecting’ the length of a DNA sequence. Once it finds its specific recognition sequence, it will bind to the DNA and cut each of the two strands of the double helix at specific points in their sugar -phosphate backbones. Each restriction endonuclease recognises a specific palindromic nucleotide sequences in the DNA.

These are groups of letters that form the same words when read both forward and backward, e.g., “MALAYALAM”. As against a word-palindrome where the same word is read in both directions, the palindrome in DNA i.e  a sequence of base pairs that reads same on the two strands when orientation of  reading is kept the same.

For example, the following sequences reads the same on the two strands in 5' à 3' direction. This is also true if read in the 3' - 5' direction.

5' —— GAATTC —— 3'

3' —— CTTAAG —— 5'