With respect to DNA, a palindrome is a segment in which the sequence is the same on one strand read right to left as on the other strand read left to right; thus, a back-to-back pair of inverted repeats.

For example, the double-stranded sequence below,

GGCGCGCC
CCGCGCGG

is a palindrome. Note that the standard definition of a palindrome (a word or phrase that reads the same backwards or forwards - e.g., RADAR) is slightly different than the way the term is used here.