1) Any DNA molecule capable of autonomous replication within a host cell and into which other DNA sequences can be inserted and thus amplified. They are or are derived from plasmids, bacteriophages, or viruses and are used for transporting foreign genes into recipient cells. Genetic vectors possess a functional replicator site and contain genetic markers to facilitate their selective recognition.

2) A vector is any vehicle, often a virus or a plasmid that is used to ferry a desired DNA sequence into a host cell as part of a molecular cloning procedure. Depending on the purpose of the cloning procedure, the vector may assist in multiplying, isolating, or expressing the foreign DNA insert.

3) A self-replicating DNA molecule that transfers a DNA segment between host cells.