The term is used mostly in the US and it describes the stages a potential buyer needs to go through to end up purchasing the product, sometimes known as a funnel.

A - Attention
The product must be brought to the attention of the buyer (often substituted for awareness)

I - Interest
To raise interest the buyer must be shown the advantages of the product vs competitors. This differs slightly from some less focused approaches where the benefits are demonstrated, even if they are equal to the that of the competition. For example demonstrating an orange juice is fresh is the same as all other freshly squeezed orange juice, however stating it is the only one with a specific type of orange which is the tastiest is showing an advantage.

D - Desire
The salesperson must create desire of the product by the buyer by demonstrating how it would fit into and improve the buyer's life

A - Action
Finally the salesperson must direct the buyer towards actually taking action and purchasing the product