CRM Selection Filters
Each Dynamic CRM entity has a set of public views. Such public views retrieve data by using a specific filter. These filters can be used in synchronization scenarios.
Each CRM->E synchronization rule has an option “CRM Filter”. Expand it to see a list of available public views.
E.g. the list of public views for filtering Contact entities:

If a specific filter is selected then synchronizer works only with those records which pass this filter.
Note: Synchronizer ignores columns configured for a public view and always retrieves all values that are required for synchronization.
See also:
- Create or edit a public view for an entity\ http://rc.crm.dynamics.com/RC/2011/en-US/online/5.1_CTP/help/source_cust_entity_Views.htm