It is extremely important to understand the type & importance of every bug detected during the testing & its subsequent effect on the users of the subject software application being tested.

Critical – is the most dangerous level, which does not permit continuance of the testing effort beyond a particular point. Critical situation can arise due to popping up of some error message or crashing of the system leading to forced full closure or semi closure of the application. Criticality of the situation can be judged by the fact that any type of workaround is not feasible. A bug can fall into "Critical" category in case of some menu option being absent or needing special security permissions to gain access to the desired function being tested.

High – is a level of major defect under which the product fails to behave according to the desired expectations or it can lead to malfunctioning of some other functions thereby causing failure to meet the customer requirements. Bugs under this category can be tackled through some sort of workaround. Examples of bugs of this type can be mistake in formulas for calculations or incorrect format of fields in the database causing failure in updating of records. Likewise there can be many instances.

Medium – defects falling under this category of medium or average severity do not have performance effect on the application. But these defects are certainly not acceptable due to non-conformance to the standards or companies vide conventions. Medium level bugs are comparatively easier to tackle since simple workarounds are possible to achieve desired objectives for performance. Examples of bugs of this type can be mismatch between some visible link compared with its corresponding text link.

Low - defects falling under low priority or minor defect category are the ones, which do not have effect on the functionality of the product. Low severity failures generally do not happen during normal usage of the application and have very less effect on the business. Such types of bugs are generally related to looks & feel of the user interface & are mainly cosmetic in nature.