A concept in behavioural economics, which suggests that positive reinforcement and indirect suggestions as ways to influence the behaviour and decision making of groups or individuals.

Most consumers do not have the time or knowledge to make entirely rational choices and instead tend to operate on automatic programming.  From a non academic point of view we are also 'creatures of habit'.   

Nudge theory is used to increase the take up of such options by making e.g. organ donation the default position, unless the patient actively chooses to opt out of the system.  This 'subtle' change brought about a significant rise in patients donating their healthy organs.

The first identified was transparency - are consumers aware of the nudge? Secondly what are the consequences of the nudge psychologically, for example might their be spillover effects in terms of consumers regretting the choices they made later? 

This is because it allows governments to influence behaviours without actually mandating them - an example being the wearing of face masks (generally made compulsory in Asian nations but remained a recommendation in many European ones). 

When businesses offer free trials which could apply to the markets for subscription services such as Netflix or magazines / newspapers.  

All of the above use loss aversion tactics - the first two offer an initial 'trial' period where the product is available either free or at a discounted price to get consumers hooked on the purchase before charging the full price.  The last two (Spike and Guardian) are available free for an unlimited time but consumers are then sent a message asking them to donate to ensure that the service continues to be offered.

By using plain speaking language to inform customers of their purchasing decisions e.g. electricity meters that tell you must money you have spent or phone apps that tell you how many calories you have burnt.  These offer positive reinforcement that encourage desirable consumption habits.