Usability expert Jakob Nielsen has defined Usability, as “Usability is a quality attribute that assesses how easy user interfaces are to use  . The term “usability” also refers to methods for improving ease-of-use during the design process.”  According to the researcher usability is defined by five quality components.
They are as follows:
- Learning ability: How easy is it for the users to accomplish basic tasks for the first time they encounter the design?
- Efficiency: Once users have learned the design, how quickly they can perform tasks?
- Memorability: When the users return to the design after a period, how easily can they reestablish proficiency?
- Errors: How many errors do users make, how severe are these errors and how easily they can correct these errors?
- Satisfaction: How much the user is satisfied with the design?
However, the definition from ISO 9241-11 which stated usability as “the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use ”
There are certain usability evaluation methods like Heuristic Evaluation, Cognitive Walkthroughs, Formal Usability Inspections, Pluralistic walkthroughs, feature inspection, consistency inspection and standard inspection . However, Heuristic Evaluation and Cognitive walkthrough are considered to be the most actively used researched techniques .
Researchers , ,  argued that heuristic evaluation has some serious usability problems. Some other reasons of not performing laboratory usability testing are the company’s lack of funds, planning or human factors. Moreover, in the experiment it is found that heuristic evaluation is better than Cognitive walkthroughs for predicting laboratory results  . Number of researches have been conducted in the Cognitive Walkthrough in next sub section present a related research and overview of the Cognitive Walkthrough method.
Cognitive walkthrough is a usability inspection method that evaluates the design of a user interface based on a cognitive model of learning and use . The cognitive walk-through compromises of two phases one is preparatory and other is analysis phase. In the first phase, the experimenters get familiar to the interface to be used, which mainly includes the users, tasks and actions to be considered during the tasks. In the analyses phase, the experimenters apply four steps of human-computer interaction which are developed by Lewis and Polson , . They are as follows:
- The user sets a goal to be accomplished within the system,
- The user determines the currently available actions,
- The user selects the action that they think will help in getting closer to the goal,
- The user performs the action and evaluates the feedback given by the system.
Heuristic Evaluation (HE), which is also known as “evaluation through expert analysis”, is a usability inspection technique . This technique was first introduced by Nielsen and Molich in 1990 . Heuristics are a set of rules, which are used to identify usability problems in the design. Heuristic Evaluation is performed by a small set of usability experts.
HE is the most widely used inspection method because it is less expensive, fast and easy to use  . A survey has been conducted in 2007, from the 1500 respondents related to the field of usability. It has been found that more than 70% of the people used the heuristic evaluation method. HE identifies more problems than user testing. HE is accurate in finding relevant problems than any other evaluation techniques   . in the next section, a search engine review is provided.