The "AND" and "OR" are the criteria options which may be used in our help desk while creating Mail Parser Rules, Notifications, and SLA Plans.
All the criteria that are inserted using “AND” are mandatory to meet from that set of criterias.
All criteria that are inserted using “OR” specify that either of the criteria in the set are met.
Using a combination of "AND" and "OR" options, the "AND" is used to collate criteria that are mandatory and the "OR" option may be used to specify the criteria from which either one of them may be used.
For example :
Status Equal To On Hold AND
Department Equal To Sales OR
Department Equal To Support
The above example implies that the 'On Hold' Status is mandatory, and the Department may be Sales or Support.