A circRNA (circular RNA) is a single-stranded RNA produced by non-sequential reverse splicing of an exon, an intron, or both. circRNA is a highly stable form of non-coding RNA and may be more stable than most linear RNAs in cells because of their nuclease resistance. Recent studies have shown that circRNA has evolutionary conservation in plants, animals, and humans, and has important biological functions. And like many other alternative non-coding isoforms, the biological function of most circRNAs is unclear.