Vectors are living organisms that can transmit infectious diseases between humans or from animals to humans. Many of these vectors are bloodsucking insects, which ingest disease-causing microorganisms during a blood meal from an infected host, which can be a human or an animal. Later, when they sting another human or animal, they inject these microorganisms into a new host during their subsequent blood meal.
Such vectors are: mosquitoes, sandflies, triatomine bugs, blackflies, ticks, tsetse flies, mites, snails and lice.
Diseases transmitted by these vectors are called vector-borne and many Neglected Tropical Diseases are exactly this: vector-borne.