A satellite is a subviral agent that depends on the coinfection of a host cell with a helper virus for its replication. Satellites can be divided into two major classes: satellite viruses and satellite nucleic acids. Satellite viruses, which are most commonly associated with plants, are also found in mammals, arthropods, and bacteria. They encode structural proteins to enclose their genetic material, which are therefore distinct from the structural proteins of their helper viruses. Satellite nucleic acids, in contrast, do not encode their own structural proteins, but instead are encapsulated by proteins encoded by their helper viruses. The genomes of satellites range upward from 359 nucleotides in length for satellite tobacco ringspot virus RNA (STobRV).

Tobacco virtovirus 1, informally called Tobacco mosaic satellite virus, Satellite tobacco mosaic virus (STMV), or tobacco mosaic satellite virus, is a satellite virus first reported in Nicotiana glauca from southern California, U.S.. Its genome consists of linear positive-sense single-stranded RNA.