Dimension items selection rules are rules to include/exclude dimension items for a program line based on dimension attributes.
For each program line, inclusion and exclusion rules can be configured for each dimension collection. Each rule contains criteria for each attribute on the dimension and includes/excludes all items from the collection which match the given criteria. You can use either AND or OR logic when selecting multiple attribute values, to specify whether items must match ALL values you've selected OR just one.
If an item is added to the collection which matches the criteria, then it will automatically be included in the program line. Similarly, if an item matching the criteria is removed from the collection, it will automatically be removed from the program line.
For more information click here.