AND condition
Every AND condition must be met for each contact that is available in that smart list.
Example: Contacts with a specific tag also having both an email AND a phone
OR Condition
At least one OR condition must be met for each contact that is available in that smartlist.
Example: Contacts having either an email OR a phone OR having a certain tag
AND and OR Combined
Groups of AND filters can be used with the OR condition among them for higher customization in filtering.
Example: Contact having both an email AND phone OR just an address
All the internal operators like IS, IS NOT, IS EMPTY, IS NOT EMPTY, CONTAINS, DOES NOT CONTAIN etc are not available for all filter fields yet.