In biology, the term "vector" can have different meanings depending on the context of use. Here are some of the most common definitions:

• Molecular biology: A vector is a DNA molecule, often a plasmid or virus, that is used as a vehicle to carry a particular DNA segment into a host cell as part of a cloning or recombinant DNA technique. The vector typically assists in replicating and/or expressing the inserted DNA sequence inside the host cell).

• Vector-borne diseases: A vector is a living organism that transmits an infectious agent from an infected animal to a human or another animal. Vectors are frequently arthropods, such as mosquitoes and ticks, that can carry pathogens that can multiply within their bodies and be delivered to new hosts, usually by biting. Diseases transmitted by vectors are called vector-borne diseases.

• Pollination biology: A vector is an organism that helps another by transporting its reproductive structures so that fertilization can occur. These are pollination vectors and are usually called pollinators.

• General biology: A vector is any biotic or abiotic agent that assists organisms in the transportation of a substance from one place to another. For example, a bee that serves as a vector in transmitting pollen to the stigma of a flower.

In molecular cloning, vectors are particles used as a vehicle to artificially carry a foreign nucleic sequence, usually DNA, into another cell, where it can be replicated and/or expressed. The four major types of vectors are plasmids, viral vectors, cosmids, and artificial chromosomes. Of these, the most commonly used vectors are plasmids. Common to all engineered vectors are an origin of replication, a multicloning site, and a selectable marker).