Xenobiology (XB) is a subfield of synthetic biology, the study of synthesizing and manipulating biological devices and systems. Xenobiology derives from the term xenos, which means "stranger, guest". Xenobiology describes a form of biology that is not (yet) familiar to science and is not found in nature. In practice it describes novel biological systems and biochemistries that differ from the canonical DNA-RNA-20 amino acid system (see the classical central dogma in molecular biology). For example, instead of DNA or RNA, XB explores nucleic acid analogues, termed Xeno Nucleic Acid (XNA) as information carriers. It also focuses on an expanded genetic code  and the incorporation of non-proteinogenic amino acids into proteins.