Any of various extremely small, often disease-causing agents consisting of a particle (the virion), containing a segment of RNA or DNA within a protein coat known as a capsid. Viruses are not technically considered living organisms because they are devoid of biological processes (such as metabolism and respiration) and cannot reproduce on their own but require a living cell (of a plant, animal, or bacterium) to make more viruses. Viruses reproduce first either by injecting their genetic material into the host cell or by fully entering the cell and shedding their protein coat. The genetic material may then be incorporated into the cell's own genome or remain in the cytoplasm. Eventually the viral genes instruct the cell to produce new viruses, which often cause the cell to die upon their exit. Rather than being primordial forms of life, viruses probably evolved from rogue pieces of cellular nucleic acids. The common cold, influenza, chickenpox, smallpox, measles, mumps, yellow fever, hemorrhagic fevers, and some cancers are among the diseases caused by viruses.
The seller, whether a solo entrepreneur or large enterprise, is a vendor, merchant, product creator, or retailer with a product to market. The product can be a physical object, like household goods, or a service, like makeup tutorials. Also known as the brand, the seller does not need to be actively involved in the marketing, but they may also be the advertiser and profit from the revenue sharing associated with affiliate marketing.

Shifting the focus to the time span, we may need to measure some "Interim Metrics", which give us some insight during the journey itself, as well as we need to measure some "Final Metrics" at the end of the journey to inform use if the overall initiative was successful or not. As an example, most of social media metrics and indicators such as likes, shares and engagement comments may be classified as interim metrics while the final increase/decrease in sales volume is clearly from the final category.
Your employees are your greatest ambassadors. If they are endorsing your product it shows that the company is taking good care of them and they have good faith in the product too. Many companies provide incentives to employees for promoting their products. In banks, clerical staffs are given monetary incentives to promote some saving schemes or mutual funds. The best performers among them may be periodically recognized by giving a gold coin on a monthly or quarterly basis.

According to a paper by Duncan Watts and colleagues entitled: "Everyone's an influencer",[66] the most common risk in viral marketing is that of the influencer not passing on the message, which can lead to the failure of the viral marketing campaign. A second risk is that the influencer modifies the content of the message. A third risk is that influencers pass on the wrong message. This can result from a misunderstanding or as a deliberate move.