Application Setting variables are the reusable constant values which will be maintained at the site level. The application setting variables make sure that the values are defined once and can be used across all the forms in the same site.
Common use of the application setting variables are to store most used string values like confirmation message for saving, deleting or updating a record. There can also be certain values that are used in more than one form which can be stored in the application settings.
The application variables can be used in validation messages, confirmation messages, values of any control, etc. You need to define the message once and use the application settings variable name everywhere where you need this message.
The link to manage Session Variables is available in the left navigation as shown in the image below.