In it’s simplest form a Viral Loop is term used for growing your product via referrals.

For example, person uses product -> tells friend -> the friend uses the product -> tells another friend who uses the product -> cycle is repeated.

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Defining the viral loop served the purpose of showing how a product might grow sustainably and allow teams to visualise how they might begin to implement a viral element into their product.

Viral loops can happen organically but most of the time companies choose to instigate viral growth by altering the product in some way.

A couple of good examples would be…

1. Uber: £10 off you and your friends next ride for a successful referral
2. Dropbox: Free extra storage MB for referring a friend / friends
3. MONZO Bank: Viral waiting list, top 1,000 referrers get free bank card and early access to BETA

There are other viral elements which determine the effectiveness of your Viral-Loop such as the Viral Coefficient & Cycle time.

Viral Coefficient: A measure of Virality

Cycle Time: The average time it takes to complete a viral-loop.