A DNA molecule (e.g. plasmid) that is able to replicate in two different host organisms and can therefore be used to 'shuttle' or convey genes from one to the other.
Source:
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 165 (https://doi.org/10.1351/pac199264010143)