The spreading of digital content, such as images, videos, or links, in a short period of time through online media such as Social Networking Sites (SNSs) and electronic mail,  shared by a large number of people (Nahon & Hemsley, 2013).

What is virality?

Virality is related to “the astonishing speed and scope with which often “empty” (i.e. not a priori determined) signs circulate online.” (Varis & Blommaert, 2015). According to Hemsley & Mason, virality is as ' word-of-mouth-like cascade diffusion process wherein a message is actively forwarded from one person to other, within and between multiple weakly linked personal networks, resulting is a rapid increase in the number of people who are exposed to the message. (Hemsley & Mason, 2013).  

Hemsley & Mason identify three key attributes of virality (Shifman, 2014:55): 

1. person-to-person mode of diffusion
2. great spead in diffusion enabled by the affordences of social media
3. broad reach. 

Typical of virality is that non-in tended audiences can be reached through algorithmic operations. Imagine you sending a tweet or posting an Instagram update, directed to your community of followers on that medium. The tweet or update will go viral when it reaches large numbers of individuals who are not included in your own community of followers. This is due to machine-generated operations in which features such as thematic content, hashtags, perceived interest among friends-of-friends or algorithmically composed "similar" user profiles ensure that the message also becomes accessible to such secondary audiences. 

Digital content that went viral is usually called a 'viral'. To many people, virals and memes are synonyms. Analytically speaking, virals and memes have very common characteristics (fast diffusion accross networks, enhanced by social media, ...) but there are important differences. The main difference between memes and virals relate to variability. Whereas virals 'comprise a single cultural unit (such as a video, photo, or joke) that propagates in many copies, an internet meme is always a collection of texts.' (Shifman, 2014: 56). 

In reality the difference between virals and memes is  fluid. Many memes are adaptations of a viral video or image macro. Memes and virals are thus two ends of a dynamic spectrum. 

References

Hemsley, J. & MAson, R. (2013). The nature of knowledge in the social media age: Implications for knwoledge management models. Journal of origanizational computing and electronic commerce 23, no 1-2 '2013): 138-176.

Nahon, K & Hemsley, J. (2013). Going Viral. Polity Press, UK.

Varis, P., & Blommaert, J. (2015). Conviviality and collectives on social media: Virality, memes, and new social structures. Multilingual Margins 2(1), 31-45.