What is the difference between Severity and Priority of a bug ?

Answer 1

Severity of a defect is related to how severe a bug is. Priority of a defect is related to how quickly a bug should be fixed and deployed to Prod users.
There may be following types of bugs

1. High severity low priority bug
   Eg: customers who use very old devices cannot continue with few features. Because the number of customers with very old devices is very low, it is not a high priority to fix the issue

2. Low severity high priority bug
   Eg: logo of company is not displayed properly in a page

3. High severity high priority bug
   Eg: login of site is not working

4. Low severity low priority bug
   Eg: Privacy policy link not working in a page

Answer 2

Severity is defined as the degree of impact a defect has on the development or operation of a component application being tested. Priority is defined as the order in which a defect should be fixed. Higher the priority the sooner the defect should be resolved.

Answer 3

Severity: If a bug cause production damage such as no users are able to access the system due to which that client's productivity is taking a hit is know as Severity and the severity's are categorized with different buckets, i.e Severity-1,2,3 & 4 and based on the severity level the issue will be action and addressed.

Priority Bugs: A bug which is causing damage to some functionalities such as the report not showing the right data, unable to process certain task due to sudden behavior change in the application, some of the functionalities are responding and etc. These are considered as priority bugs which a company will prioritize the priority to fix the issue so that client can do their business with no hassle.

Answer 4

Both Severity and Priority are attributes of a defect and should be provided in the bug report. This information is used to determine how quickly a bug should be fixed.
Priority by the English definition is used in the comparison of two things or conditions, where one has to be given more importance than the other(s) and has to be tackled with/resolved first before proceeding to the next one(s).
Therefore, in the context of defects, the priority of a defect would indicate the urgency with which it would need to be fixed and deployed to live servers
Severity by the English definition is used to describe the gravity of an undesirable occurrence.
Hence when it comes to bugs, the severity of a bug would indicate the effect it has on the system in terms of its impact. Usually the severity is defined in terms of financial loss, damage to environment, company’s reputation and impact on end user.
When a defect is of high severity, most likely it will also have a high priority. Likewise, a low severity defect will normally have a low priority as well.

Below are some examples for more understanding 

High Severity – High Priority bug
This is when major path through the application is broken, for example, on an eCommerce website, every customer gets error message on the booking form and cannot place orders, or the product page throws a Error 500 response.
High Severity – Low Priority bug
This happens when the bug causes major problems, but it only happens in very rare conditions or situations, for example, customers who use very old browsers cannot continue with their purchase of a product. Because the number of customers with very old browsers is very low, it is not a high priority to fix the issue.
High Priority – Low Severity bug
This could happen when, for example, the logo or name of the company is not displayed on the website. It is important to fix the issue as soon as possible, although it may not cause a lot of damage.
Low Priority – Low Severity bug
For cases where the bug doesn’t cause disaster and only affects very small number of customers, both Severity and Priority are assigned low, for example, small spelling mistakes on privacy policy page. Not many people view the privacy policy page and so these spelling mistakes doesn’t affect the customers much.