The attitude that the user develops as a result of previous experience with similar products/service or previous experience with the product/service in question that evolves over time. Tag must be used only when there's a change or shift in an otherwise common user expectation.

User expectations refers to the consistency that users expect from products. Interaction design is very concerned with this topic. Note that user expectations can shift over time, similar to what is described in the Kano model of customer satisfaction.

A good rule of thumb or design principle to use in interaction design is to follow the "Principle of least astonishment".

In the case of interactive software applications, for example, users form expectations based on their experience with similar kinds of software. Effective software design aims to conform with prevailing norms for aspects of behavior such as the software's user interface and its respons

http://en.wikipedia.org/wiki/User_expectations