Palindromes are sequences which read the same forwards and backwards.
 

• If the sequence is composed of letters, the simplest example is "MOM".  Others are:
• DUD DUDE
• TACO CAT
• ABLE WAS I ERE I SAW ELBA   (attributed to Napolean)

 
• If the sequence is composed of DNA nucleotides:

5' ---> 3'
GAATTC        EcoRI
CTTAAG
3' <--- 5'

5' ---> 3'
CTGCAG        PstI
GACGTC
3' <--- 5'