CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats and a CRISPR sequence refers to a DNA locus with hallmark features including, repeated palindromic sequences, which is part of an adaptive immune system in bacteria and a system that has been adapted for use in genome editing and other applications using CRISPR/Cas Tools.
From the CRISPR palindromic sequences, RNA molecules are transcribed and adopt a stable secondary structure between 23 and 47 base pairs in length. Variable regions called spacer DNA are located between these sequences which originate from the genome of foreign DNA. The spacer sequence or protospacer adjacent motif (PAM) is required for target recognition.